Rare Earth Revelry two: Incompatibility and rare earth patterns

As I explained in the last Rare Earth Revelry, the ionic radius of the Rare Earth Elements decreases in a systematic manner with atomic number (figure 1, revisited).

Figure 1. ionic radii of various REE and other elements (repeated from last time).

As you can see, the ionic radii for aluminum and magnesium are quite small. Silicon (not shown) is smaller still. So the magnesium/silicon/aluminum minerals that make up the bulk of the Earth’s mantle have difficulty fitting the large REE into their structures. However, the mantle also contains calcium minerals, and this allows some of the REE, particularly the heavier ones, to squeeze into a calcium site under some circumstances.

When the mantle melts, the melt has a much more fluid structure than the minerals, so it can accommodate the REE more easily. This means that during partial melting ,the REE generally partition into the melt relative to the residual minerals.

The ratio in which an element partitions into melt vs. residual crystals is known as its compatibility, and is represented by something called a D value. The D value is the ratio of the concentration of an element in the mineral relative to the concentration in the melt.

An element with a D value higher than one is compatible; it tends to remain in the mineral. An element with a D value less than one is incompatible. D values depend on the minerals present during melting, but under most circumstances, the REE are incompatible, and the light REE are more incompatible than the heavy REE.

The degree of the difference in compatibility between the light and heavy rare earth depends on the degree of melting, and the exact minerals present in the residue. Garnet residues, in particular, tend to hang on to the heavy rare earth elements while excluding the light ones.

Some examples of this can be shown in figure 2.

Figure 2. The REE pattern of a lunar anorthosite (blue line), compared to some terrestrial rocks. From the wustl meteorite pages

This figure, from the lunar crust, shows the REE pattern of feldspar crystallized from the lunar magma ocean (blue line). The REE pattern is almost flat. In contrast, garnet is present in the deep terrestrial mantle where the magmas that bring diamonds to the surface form. Figure 3 shows the rare earth element pattern for one of these magmas, called a kimberlite.

Figure 3. The REE pattern of a kimberlite. From Le Roex et al.

The relative incompatibility is important for understanding the composition and economics of rare earth element mines, as will be discussed next week.

Rare Earth Revelry
Week -1
Introduction
Week 1
Week 2
Week 3
Week 4

SHRIMP volume out

The special SHRIMP issue of Precambrian Research came out last month, and is available here. Anyone interested in how a large ion probe named after a small crustacean facilitated the understanding of the first 90% of Earth history might wanna take a look.

Some seasonal suggestions for saving the snow

Although this trend may not be apparent for this week’s current weather patterns, the northern winters are getting warmer. While the optimists among us may feel that eventual progression from carbon-based energy sources to some other technologies may help resolve this problem, it is unlikely that such a transformation will be made anytime soon. So unless we all want to melt Greenland, some additional measures should probably be taken to keep the north pole cold.

Such geoengineering proposals are often contentious. However, properly framing them may reveal surprising levels of support for modest measures. Here are two examples.

1. Clear the taiga. The boreal forest is a huge expanse of cold-climate conifer trees, which inhabit terrain that was either glaciated or tundra during the last ice age. These trees are adept at absorbing the springtime sun, and replacing them with flat, reflective snow would hopefully postpone the spring thaw. As the trees are a potential source of building and paper raw materials, cutting down the existing forests ought to pay for itself. However, should seedlings in these areas be allowed to regrow, then they would become a thicket of sub-economic sized trees which would still protrude from the snowpack. So a yearly cull of small conifers would be in order, to keep the flat ex-forested plains flat and snowy. Supporters of this idea could assist in this by creating a market for small felled conifers. As such trees lack inherent utility, they could potentially become decorative items, to be lit up by representations of the boreal winter’s 24 hour stars. Supporters of this proposal could signal their support by displaying a small severed conifer in their homes during the time period leading up to the northern winter solstice.

2. Eliminate the ozone. Ozone is a greenhouse gas. It traps heat in the atmosphere that would otherwise escape into outer space. It also adsorbs UV light, so simply eliminating all of it would make the surface of the earth uninhabitable. But during the polar winter, there is no solar UV to block, so a temporary elimination of ozone in the middle of winter would allow cooling without the complications associated with destroying the entire layer.

Trouble is, our current system of ozone destruction using chlorofluorocarbons does not work during the winter- it works in the spring, once the sun has come up. So some other method, such as aerosolizing a solid ozone-destructing catalyst (like this) would have to be used, so that the catalyst would be out of the system by springtime.

Even so, there would be a temporary increase in UV as the ozone layer rebuilt during the arctic spring. And this would have a carcinogenic effect on northern animals, especially their exposed body parts, like noses. Still, giving a few reindeer cancer may be the price we have to pay for saving the planet, so I suggest anyone who things this is a good deal should display picture or statues or reindeer with swollen, cancerous red noses.

Although geoengineering can be contentious, canvassing the level of support for these particular suggestions should be easy. Simply look for homes where severed conifers or cancerous reindeer are being celebrated and displayed, and if such places are common, then the obvious interpretation is that the inhabitants of such houses are in favor.

See also: Santa boycotts coal.

Where is everyone?

I've been busy running two SHRIMPs all week, and I gotta explore a new isotopic system on one of them this weekend. So I won't have a REE update this week. In the mean time, I have a question for any other bloggers who read this. Have you moved this year, and if so, where to? I realize my link list is hopelessly out of date, but put your new url in comments and I just might update over christmas break.

Young rocks

Evy, the skepchick who is now geoblogging at georneys, recently expressed surprise at a paper which labeled rocks with an nine digit age as young. I see nothing wrong with this, however. Depending on how you define 'beginning', the Earth is between 4567 and 4460 million years old. using 4500 as a convenient round number, we can then take half that as a midpoint, and place the old rock / young rock divide at 2250 MA. Alternatively, we could lash out and use 1.5 billion year divisions to call rocks old (> 3.0 Ga), middle-aged (between 3 and 1.5) and young < 1.5 billion.

In Gondwanaland, the 1.2-1.0 Ma Grenville orogeny is much less prevalent than it is in laurentian rocks. It shows up here and there, but is not a major event. The middle proterozoic was in fact fairly quiet in Gondwana, with the Neoproterozoic-to-Cambrian Pan-African / Brasiliano / Ross orogens being the defining tectonic events that assembled the various pieces of Gondwanaland into the supercontinent that we all know and love. So for those of us interested in the pre-assumblage history of Gondwana, it makes perfect sense to describe anything after the midproterozoic as young. I even did so in my thesis, in this sketchmap of the geology of the Brazilian state of Bahia:

Rare Earth Revelry, week one

As I mentioned in the introduction, the Rare Earth Elements (known to chemists as lanthanides) are an esoteric yet commonly studied group of elements. The reason they are studied is that both their behavior as a group, and the more subtle change in behavior between the different rare earth elements can reveal information about the system in which they are observed.

The REE are refactory lithophile elements, meaning that for the most part they condensed at high temperature in the solar nebula as oxides*, and thus have similar behavior to calcium and aluminum during the planet-forming process.

In nature, the REE on earth generally form large, 3+ cations in a variety of complex oxides (figure 1). They are most commonly found as trace elements in silicates, but are readily concentrated in phosphate minerals. They rarely occur as carbonates.

Figure 1. ionic radii of the REE and selected other elements. Data from Shannon & Prewitt (1969), via the web. REE are light blue, comparison trivalent cations are dark blue. Divalent ions are green, with light green for Eu. Tetravalent cations are red, with pink for Ce. pdf available on request.

The ionic radius of the REE decreases with increasing atomic number, so that lutetium is about 20% smaller than lanthanum. The heavy rare earth elements (HREE) are similar to yttrium, but are still substantially larger than other common rock-forming trivalent elements (figure 1).

Although all REE are generally trivalent, two of them have other valence states that occur in nature. Europium can have a +2 valence under moderately reducing conditions, which makes it behave much like the element strontium (figure 1). Under oxidizing conditions found in surface processes on the modern Earth, cerium can be tetravalent, and Ce+4 has a size intermediate between zirconium and uranium.

In general, the large ionic radius makes the REE incompatible in most mantle mineral lattices (which are comprised mostly of Mg, Si, Al, and Ca). So mantle melts are enriched in REE relative to the residual mantle. The continental crust in enriched further still relative to the oceanic crust. However, the larger light rare earth elements are more incompatible than the more compact heavy rare earths. The degree of incompatibility is related to the minerals present in the mantle when it melts, so the pattern of REE in igneous rock at the surface can give us a clue as to what minerals are present deep in the inaccessible part of the Earth where the melting occurs.

Ref:
R. D. Shannon and C. T. Prewitt, Acta Cryst., 1969, B25, 925

Rare Earth Revelry
Week -1
Introduction
Week 1
Week 2
Week 3
Week 4

* We’re ignoring enstatite chondrites for now. I’ll come back to them another time.

Pie crust phase equilibria: update

Four years ago, I posted the basics on the phase equilibria of pie crust in this blog. A summation of that post, as well as an update, appears below:

With American Thanksgiving and Christmas rapidly approaching, the pie baking season is rapidly approaching. One of the most important, but least quantified, aspects of pie creation is the crustal composition. A simple ternary phase diagram for three-phase pie crust is presented below.

While the “traditional composition” point is plotted to scale, the positions and shapes of the curve are poorly constrained approximations. Lack of accurate thermodynamic data for the system precludes accurate prediction of these fields. It is the shapes and positions of the top two curves that is of paramount importance; anyone who reaches the butter-water two phase field should be banished from the kitchen.

As anyone with baking experience knows, the stability region for pie crust is a relatively small area on the wet side of the two phase flour + dough field. This field is generally approached by adding water to a flour/butter mixture, as is shown below.

Four years ago, I suggested the following approach:

However, if the approximated slopes shown above are correct, then a radical new approach to crustal formation might be advisable. By generating a flour-water mixture, and then adding butter, a wider range of valid crustal compositions should be achievable before exiting the edible portion of this phase diagram. This approach is shown below.

In hindsight, this was silly. There are two reasons. Firstly, accurately ganguing the initial water/flour mixture is difficult, as your starting composition is in the 2 phase flour water field. And secondly, this procedure generates a crust with the minimum possible butter, and butter is yummy. So this year, I will endeavor to explore the left hand side of the diagram. I suspect that the dough / slime boundary curves over a bi farther than is illustrated here.

Rare Earth Revelry: Week -1

Ladies and gentlemen, welcome to week -1 of the Rare Earth Revelry. That is not a dash folks, this is week negative one. Why start here? Because we are starting before the beginning. We are turning the clock back 5 billion years to discuss rare earth elements in stars that died before the Earth was formed.

Cosmologists tell us that the universe started out with no heavy elements in it; all the carbon, oxygen, silicon, and everything else was formed in stars, a byproduct of the energetic reactions that makes stars shine.

The exact details on nucleosynthesis, the manner in which the elements of the periodic table came to be, were worked out in theory in the middle to end of the 20th century. For elements heavier than iron, there are two main mechanisms, both of which involve neutron capture.

In large, elderly stars, after the hydrogen fuel of the main sequence is exhausted, the star turns to burning helium. There are numerous reactions between helium nuclei and those of heavier elements, and some of these (e.g. ²¹Ne + ⁴He -> ²⁴Mg + n) produce neutrons.

In the S process (S for stellar), heavy elements grow heaver by absorbing neutrons produced in such a manner. However, the flux of neutrons is fairly low, so that if neutron capture results in the formation of an unstable nucleus, that nucleus generally has time to beta decay into something more stable before the next neutron capture.

For the light rare earth elements, this process is illustrated in figure 1.

Figure 1. S process formation of Nd isotopes. X axis is number of neutrons in nucleus, Y axis is number of protons. Figure generated from NuDat 2.5

It generally takes a few million years for a star to chew through its helium, after which the process stops. Helium burning can be a fairly unstable process, so these stars can mix their core material up into their atmospheres, (called “dredge-up”) and then blow their atmospheres off into space, allowing the elements to escape.

The S process has a few drawbacks, specifically its inability to explain a number of heavy isotopes, as well as the elements uranium and thorium. If you add a neutron to ²⁰⁹Bi, to form ²¹⁰Bi, the ²¹⁰Bi decays into ²¹⁰Po, the isotope used to kill Viktor Litvinenko. ²¹⁰Po alpha decays back down to ²⁰⁶Pb, so you can’t get up to mass 232 or 238. Also, as shown in Figure 1, ¹⁴²Ce, ¹⁴⁸Nd, and ¹⁵⁰Nd cannot be produced by the S process.

The R-process (R for rapid) explains these elements. In the R process, an extremely high neutron flux means that nuclei absorb neutrons faster than they can decay. (figure 2)
Because there is no time for decay, the instability gap between polonium and thorium can be bridged, and actinides, as well as heavy isotopes of other elements, can be formed by this process.

Figure 2. R-process for Nd isotopic formation. Note that ¹⁴²Nd is not formed in this process.

In the case of neodymium, ¹⁴²Nd can only be formed by the S process, ¹⁴⁸Nd and ¹⁵⁰Nd can only be formed by the R process, and 143-146 can be formed from both.

The bulk solar (and meteorite, and planetary) isotopic composition can be 99% explained as a mix of S process and R process isotopes, suggesting that the gas cloud that collapsed to form our solar system contained the remnants of both supernovas and material expelled from old, evolved stars.

From the 1950’s onward, that was the theory, and it was a nice theory. But there is one more thing we need to know about the theory before letting it loose on real rocks.

As the S process requires a star to have entered the helium burning phase of its life, there is another compositional change that occurs. Stars like the sun have about twice as much osygen as carbon in them. But helium burning produces carbon, so in some helium burning stars, there is more carbon than oxygen. This is important, because if a carbon rich atmosphere gets ejected, the excess carbon means that instead of just forming carbon monoxide gas, condensates of carbide such as SiC can form.

In the late 1980’s, researchers working with primitive meteorites discovered that they contained trace amounts of tiny silicon carbide grains. It was hypothesized that these might be dust from carbon-rich helium burning stars, which avoided getting remelted in the primordial solar nebula. So, in the early 1990's, the Nd isotopes were measured. And what did they find?

All the Nd in the silicon carbide was S-process only. Just like the theory predicted.

Figure 3. S-process Nd in presolar SiC grains. Source.

Rare Earth Revelry
Week -1
Introduction
Week 1
Week 2
Week 3
Week 4

Further reading:
Zinner 1998 (fee)
Zinner et al. 1991 (free)
Guber et al. 1997 (fee)

Rare Earth Revelry

It has been an odd year for the lanthanides. After decades of sitting, quietly, in a row of their own at the bottom of the periodic table, the rare earth elements have been thrust into the limelight by numerous MSM articles.

As it turns out the REE have been a quiet favorite of geochemists for decades. They are used for everything from determining how stars make chemical elements to keeping the compact fluorescent lights on. And they are the bread and butter of numerous geochemical studies. For example, the latest issue of Geology reports rare earth concentrations in 4 of its 23 articles- and this is a general earth science publication, not a geochemistry specialist journal. Rare Earths are used to in stellar nucleosynthesis, missiles, planetary formation, phosphors, continental evolution, magnets, geochronology, neutron capture, volcanism, lasers, and gas light mantles. There is a lot to know, but I will try to start at the beginning. Their names. If you can't remember the list lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, then I suggest you use a mnemonic.

Next up, stellar nucleosynthesis, and rare earths in stars that died before the sun was born.

Rare Earth Revelry
Week -1
Introduction
Week 1
Week 2
Week 3
Week 4

Google bails on the greenback

Google AdSense to me
show details 9:19 AM (1 hour ago)
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you've recently made this change.

The main changes included in this Terms and Conditions update are:

- The party that publishers are contracting with changes from Google Inc. to Google
Ireland Limited.
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Google will only issue VAT refunds to publishers with an address in Ireland.
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Reference checking drinking game

Sip :
et al
et. al
et. al.
Inconsistent & vs. and.
Gratuitous references to common knowledge which you tracked down as a form of procrastination (e.g. Petri 1887).
Obvious misplaced fields in electronic database citation collection.
Commas instead of semicolons, or similar format errors.
Incnst. Abbrv.

Chug:
Mixed formats in bibliography.
Autoformatting that undoes manual corrections.
Crummy old Xerox copies which cut off the journal information.
Bibliography references orphaned by aggressive cuts.
References missing from the bibliography because they are only listed in figure captions, which is a different file.
Subtle misplaced fields in electronic database citation collection (e.g. page and volume numbers switched).
Correcting a reference database error in the proof, without fixing the database.
References written in non-latin alphabets.


Drain the bottle:
Referenced papers you’ve never actually read.
My reference formatter is set up perfectly, I have no need to look at the output.
Software updates delete all the corrections you performed to your reference list.
Actually reading the referenced paper only to find that it actually says the opposite of what you inferred based on the way that other people referenced it.

The night of transition metal hydroxides

All hallows eve, and children everywhere will be donning their scariest costumes and venturing out into the darkening gloom to wrest their favorite hydroxides from neighbors and strangers.

I am taking, of course ,about sweetite. Sweetite, known from a limestone quarry in England, is zinc hydroxide. I don't have the exact petrogenetic details, but I'm guessing that it was leftover from decarbonation reactions in water-rich veins. One of these years, I'll get organized enough to give out mineral specimens to the wandering children, but that may have to wait until I live in a country that actually celebrates halloween. Until then, I wish you all well, and hope you enjoy your zinc minerals. Until someone discovers, describes, and coins zombiite, it is the most suitable mineral for this holiday.

Happy Halloween.

Meteorite tea, and the failures of genius

In the early 1970’s, Io, the innermost large moon of Jupiter, was somewhat of an enigma. Unlike Europa and Ganymede, it did not exhibit water ice adsorption bands it its IR spectra. Its density suggested that it was a rock and metal planet, but the surface reflectance was unlike anything known to science. This problem was addressed brilliantly in a Science paper by Fanale, Johnson, and Matson, researchers at the Jet Propulsion Laboratory. These scientists explained all the anomalous features of Io in a single stroke of genius.

By that time, it was known that meteorites were primitive condensates of the primordial solar nebula, even though the detailed work describing their subtle differences had not yet been completed. Since the outer moons of Jupiter were known to contain water, the study hypothesized that Io lost its primordial water and never accreted any ice later on. They then tested this hypothesis. Fanale et al. took a piece of the very primitive CI meteorite Orgueil, and made meteorite tea by boiling the piece of Orgueil in water. They then evaporated off the water and looked at the precipitate. What they found was mostly magnesium and sodium sulfate salts, with some halite and other elements mixed in. The reflectance spectra of these precipitates more closely matched that of Io than other hypothesized frosts, especially when treated with radiation. AS the evaporite was enriched in sodium, this process also efficiently transported sodium to the surface, where it can be ionized by ambient radiation, producing the Na ionization halo which was known around Io at the time.

So basically, the theory goes like this: during accretion, Io was too warm for ice to condense. Accretion from meteorites comprised of hydrous silicates released water as the planet grew and the interior increased in heat and pressure. This fluid then leached the rock, escaped to the surface, sublimed or evaporated, and left salts behind, which was what we see today. In other words, Io is an evaporite planet.

This theory explained everything know about Io so well that it would be another five years before Voyager one- at the time the most advanced robotic space probe ever launched- took pictures of Io as it flew past Jupiter which instantly and completely proved the evaporate hypothesis to be false.

The history of science is often taught as a series of breakthroughs generated by men of immense intellect who are smart enough to see the world as it is. But the reality is that the world doesn’t really care about genius. There are many incredibly brilliant scientific deductions- like the hypothesis of Fanale et al. of the evaporitic Io, which are spectacularly and brilliantly wrong. But science education has a powerful selection criteria that ignores all of the stunningly clever, but completely incorrect deductions. Instead, proponents of discarded theories are often depicted as dim, or close minded, or stuck in their ways. But in cases such as this one, they simply had no way of acquiring the data needed to disprove their hypothesis, as flying to Jupiter and looking at Io up close was science fiction in 1974. Five years later, it was history, and so was their wonderful model.

Fanale, F., Johnson, T., & Matson, D. (1974). Io: A Surface Evaporite Deposit? Science, 186 (4167), 922-925 DOI: 10.1126/science.186.4167.922

Carnival of space #173

Is here.

A few thoughts on the Hungarian Red Sludge disaster

The news has been showing pictures of an environmental catastrophe in Hungary, where a huge spill of toxic sludge from an alumina processing plant has killed several people and lots of fish. I am not an expert on alumina refining, but I’m going to take an educated guess at what happened here using geochemical first principles.

Aluminum is mined from bauxite, which contains lots of aluminum hydroxide plus other contaminant elements. These need to be removed when the ore is processed into pure aluminum oxide.

Aluminum is very insoluble under moderate pH (pdf), dissolving only in very strong acids or bases. So any purification procedure based on aqueous chemistry is probably going to use either very low or very high pH. So their bauxite ore was treated with sodium hydroxide to increase the pH to over 13.

High pH solutions are extremely caustic, and will chemically burn people fish and other organisms just like strong acids do. That is what makes this dangerous.

In addition, most toxic metals are generally more soluble than aluminum is, so any dangerous elements originally present in the ore sill stay in solution. Their concentration will depend in part on whether they accumulate during mineral processing, and how much was in the original ore. That is why they probably don’t have a good heavy metals estimate yet. The same reasoning applies to radioactive U and Th.

As this sludge reacts with things and gets less basic, the solubility of aluminum and iron (a major contaminant in bauxite) will drop, and gibbsite and goethite can be expected to precipitate. The goethite (a.k.a. “rust”) and related iron minerals give the sludge its red hue.

This is all conjecture, however, so I’d love to hear from anyone with actual knowledge.

Astronomical risk calculation

One of the greatest challenges facing media saturated democracies is the inability to correctly gauge the relative importance of catastrophic, visually impressive, rare events vs. common incremental ones. Here are some examples:

If, dear reader, you happen to die in transit, I personally guarantee that you won’t be killed in an airplane blown up by terrorists. The overwhelming odds are that you will die in your own car instead.

Similarly, if you are killed by our energy infrastructure, it won’t be nuclear meltdown that wipes you out. Chances are, you’ll have an asthma attack, or get emphysema from air pollution instead.

And as a geologist, I make the following prediction with even more confidence.

Nobody reading this blog will be killed by a meteorite impact.

It just isn’t going to happen. Fatalities from geohazards are a rare form of death anyway, but if you are unlucky enough to succumb to one, it will probably be a flood or some sort. If not, then an earthquake, or a debris flow. Asteroid impacts are far more spectacular than muddy rivers, but the big ones just don’t happen often enough to create any significant health risk. But that doesn’t stop bolide researchers from scare-mongering in order to get funding.

Just look at the second picture in this Planetary society post from last year. It is an overlay of the Tunguska event on the city of Los Angeles, showing how huge swaths of the city could be incinerated by this relatively modest sized impactor. No mention is given of the likelihood of this event. Luckily for us, though, it is easy to calculate.

Impacts are equally likely on any point on the globe. Thus, the likely hood of an impact in the city of Los Angeles is simply the area of LA divided by the surface area of the Earth. For those who don’t have the numbers on hand, this is about one in 400,000, or 2.5 out of a million. And LA is a very large city; the city limits are only slightly smaller than the state of Rhode Island. Assuming one Tunguska event every century, we’d expect to have to wait for something on the order of 20 million years for a 50% probability of hitting LA. And the rocks LA is built on aren’t even that old.

The most likely scenario for the next Tunguska-style event is for it to happen over the open ocean. And if that would occur, the effect we would see would be…
Absolutely nothing.
A satellite might see such an event. Otherwise, we wouldn’t even know it happened.

So, just for kicks, I pulled an equal area map off of the web, and hit it with 100 impacts, just to see what would happen. I’ll get into the gory details in another blog post, but just to whet your apatite, the picture is here.

The dots are about 130 km across. This is the approximate kill radius for a 400 meter rock under standard assumptions. A rock this big lands about once every 100,000 years, according to the theoreticians, so this is 10 million years worth of impacts.

In future posts I’ll look at some of the details, and what they might mean.

How do you use Wikipedia?

With the new northern school year underway, we can expect that the shorter days and colored leaved will bring with them a bevy of complaints by academic bloggers about the evils of Wikipedia and how venal students are for using it as a reference.

This does not strike me as constructive criticism. After all, Wikipedia is certainly no worse than any other encyclopedia, and it is an incredibly useful resource. So instead of whinging about it, I’m going to explain what I use it for, and when I don’t think it is much good. I challenge all the wikiwhinging professors out there to come clean and do the same.

I have two main uses for wikipedia: Looking up ‘common knowledge’, and giving myself a background on things I know nothing about.

An example of the first is the mass of Jupiter. This is a very well known constant- it is the main unit of mass for exoplanetary studies, for example. But I don’t know off the top of my head how many kg (or earth masses, which I do know) Jupiter is. Wikipedia is the easiest way to get this number, and the chances of it being wrong are quite small.

As far as the general knowledge about stuff I don’t understand, my approach is generally to read the article, then dig into the links at the end if I need to be sure of any particular facts, or need more depth. The last thing I looked up was the history of Guangzhou, and I didn’t follow it up because the interest was casual.

I would use Wikipedia for math and physics equations, except that I find it to be terribly obtuse and difficult to find simple equations or succinct descriptions.

I use the sites linked in the “useful links” part of the sidebar for technical information.

If I need to understand something in Wikipedia at a research level, I generally come up with some keywords based on the article and plug them into google scholar.

I find that Google scholar is better for keywords and titles, while georef is better for author or journal searches.

So, wikiwhingers, come clean. What do you use the masses encyclopedia for? (feel free to blog at length on your home site on this subject)

Do unemployed metamorphic petrologists...

...live in their mother's basement?

Why are minerals important?

The other day, someone (a non-geologist scientist) asked why minerals were important, and the earth can’t just be thought of as a homogenous lump of elements. Here in myopic subfield land, it sounds like a stupid question, but mineralogy and petrology do not exactly have the highest profile amount the general population. The man on the street thinks a petrologist is someone who works for Exxon. Word thinks the petrologist is a misspelling of pathologist. So I took a quick look at my old undergrad petrology textbook, and it doesn’t even consider the question. The introduction starts, “Igneous rocks are formed by the cooling and crystallization of magma, which is molten rock that”.
It then goes into definitions, and there is no attempt to even sell the field.

On a related note, when I left the ANU back in ’07, they were performing a curriculum review, and one of the ideas floated was to ditch mineralogy as a core required class. So even Earth Scientists (evidently ‘geologist’ is old fashioned, and creates insecurity among our colleagues who don’t actually know what a rock is) underappreciate the organization of atoms into ordered structures.

I got into petrology because I thought it was cool, and then strayed into geochem by inertia. But I’ve never really defended its importance before. So I’ll let all you lurkers speak up here. Consider this a hard rock version of the introduce yourself post. What is great about mineralogy and petrology, and how do you explain petrology in a sentence to someone who thinks you work for Exxon?

The lead isotope systematics of pregnancy and lactation

Isotope geochemistry is useful for so many things that its application to fetal and maternal health can be overlooked. However, this does not diminish the value of isotopic studies to this field. Consider, for example, the groundbreaking ‘Russian Bride’* experiments of Gulson et al.

Determining calcium loss and lead exposure in pregnant women is not easy. Most of the bodies calcium is stored in bones, and because lead substitutes for calcium in most minerals (biogenic or otherwise), bone hydroxyapatite can also be a potential source for lead, if bone resorption occurs. But detecting this is not always easy.

Bone density measurements can be done by X-rays, but in pregnant women this risks giving the unborn child super powers. Bone biopsies are painful and intrusive. So isotope geochemistry is a much less harmful way of measuring whether or not bone resorption is occurring, and whether or not it is contributing lead to the bloodstream.

In the study reported in these papers, European immigrant women who became pregnant a few years after migrating to Australia were studied. This is important- soft tissues exchange lead rapidly with the environment, whole bone matter can take decade to equilibrate. Most environmental lead in Australia comes from the Proterozoic Mt. Isa and Broken Hill mines. These lie on (and help define) the earth isotopic evolution curve, so have a ²⁰⁸Pb/²⁰⁶Pb ratio of about 2.23. Most Eastern European women who grew up in the Eastern Bloc were primarily exposed to Paleozoic lead with an isotopic ²⁰⁸Pb/²⁰⁶Pb ratio of about 2.10. So their soft tissues and bones should have different isotopic signatures.

Figure 1. An Australian immigrant will have different Pb isotopic signatures in bones and soft tissues.

If such a person starts to resorb bone calcium, this should also liberate Pb substituting for calcium, and the blood Pb isotopic ratio should move towards the skeletal value. This is exactly what Gulson et al. saw during pregnancy and lactation in women who did not take calcium supplements.

Refs
B.L. Gulson, C.W. Jameson, K.R. Mahaffey, K.J. Mizon, M.J. Korsch, G. Vimpani; Pregnancy increases mobilization of lead from maternal skeleton; The Journal of Laboratory and Clinical Medicine, Volume 130, Issue 1, Pages 51-62 (July 1997)

GULSON B. L. ; MAHAFFEY K. R. ; JAMESON C. W. ; MIZON K. J. ; KORSCH M. J. ; CAMERON M. A. ; EISMAN J. A. ; Mobilization of lead from the skeleton during the postnatal period is larger than during pregnancy; The Journal of laboratory and clinical medicine 1998, vol. 131, no4, pp. 324-329


GULSON, B., MIZON, K., KORSCH, M., PALMER, J., & DONNELLY, J. (2003). Mobilization of lead from human bone tissue during pregnancy and lactation—a summary of long-term research The Science of The Total Environment, 303 (1-2), 79-104 DOI: 10.1016/S0048-9697(02)00355-8
* For what it's worth, every Russian bride I knew during the time period of this study had an advanced degree in physics, and was working in Australian academia or industry to win their family's bread.

BHP calls for carbon tax

BHP, the largest mining company in Australia (and the world), is now calling for a carbon tax in Australia, according to various news sources. Like just about everyone else, I'm not really sure what to think of this, so read between the lines of the linked articles and see what insight might be gained. BHP is widely diversified, and has major holdings in export coal, export iron ore, oil & gas, uranium, aluminum, and various base and ferrous metals.

In the recent election, neither major party supported a price on carbon in the next three years, but the Greens forced the government to set up an investigative committee on the matter as a price of forming a governing coalition.

Maybe Latin ain't such a bad idea

I hate Latin- it is one of the reasons I'm not a biologist. And I love the multicultural way in which geology incorporates technical terms from all around the world. Forgot your vocab? That's fine; the Norwegian sounding words are more likely to relate to ice than the Arabic ones. Still, there are a few terms that make me wonder. After the eruption earlier this year, everyone knows about Eyjafjallajökull. But at the opposite end of the time scale, Nuvvuagittuq ain't much easier. Of course, there are alternatives, as was demonstrated at post-conference beers:
Me:
How do you pronounce Noov- Nuff- Nuvatta- That really old metamorphic belt northeast of Hudson Bay?
Canadian professor:
It is pronounced "Porpoise Cove."

Chlorine á gogo

There is a Universe Today article on the lack of organics found by the Voyager missions, which suggests that the chlorinated organics originally thought to be cleaning products could have actually been reaction products from Martian organics and Martian perchlorates (perchlorates and organic molecules react vigorously when given the chance- see the Space Shuttle’s solid rocket boosters for an example). The paper is not yet available, and I’m not a big fan of the press-release-before-publication model that NASA seems to be getting fond of these days. So I’m gonna sandbag the study based on the interview.

They say,

“One reason the chlorinated organics found by Viking were interpreted as contaminants from Earth was that the ratio of two isotopes of chlorine in them matched the three-to-one ratio for those isotopes on Earth. The ratio for them on Mars has not been clearly determined yet. If it is found to be much different than Earth's, that would support the 1970s interpretation.”

So, measure the martian Cl isotopic ratio and see in the Viking measurement is terrestrial or martian.

This is not a well designed experiment. We know from Sharp et al. (2007) that Cl isotope ratios don’t vary much either on Earth or in chondrites. One permil is 1 tenth of a percent, so a 1 permil difference is a change in 35Cl/37Cl ratio from 3.125 to 3.128. It is unlikely that the Voyager measurements are anywhere close to precise enough to see this sort of variation.

Long et al. (1993) show that surface processes on Earth change the ratio by up to 4 permil. Nakamura et al. (2009) show a similar change in Cl metabolized by organochlorine-eating bacteria. The only place Cl isotopic variations exceed 1% (ten permil) is the moon (Sharp et al. 2010), and this is due to an extremely hydrogen-poor environment (insufficient H for chlorine to volatilize as HCl when outgassing from magma) that we know doesn’t exist on Mars, as it is covered in ice and hydrous minerals.

Luckily, we have Martian meteorites. They have lots of Cl in them (Bridges et al. 2001), so we should be able to get Cl isotopic ratios for phases present in those samples. I suspect that Sharp might be doing that as we speak. But there is no reason to expect that the values will be different enough to terrestrial that they can be used to test the provenance of the Viking Cl isotopic analyses.

Choice magazine to consumers: don’t eat white dwarfs

There is a Choice Magazine report advocating for stoplight rating of foods, to help consumers eat more healthily. Their rating system uses units of 100g/mL (see figure 1, below). That is tenths of a kilogram per milliliter. I don’t know what they are eating, but the densest known substance at the surface of the Earth is osmium metal, with a density of about 22 g/mL, or 0.22 100g/mL.

Their “green light” value for sodium is 0.3 100g/mL, which is about 50% denser than anything on Earth. For comparison, a pure halite crystal 1 centimeter on a side (salt conveniently grows in cubes) will contain 2.16 g/cc x 0.39 g(Na)/g(total) = 0.85 g sodium. In units of 100g/ml, pure salt thus has a value of 0.0085 100g/mL.

Never-the-less, they rate almost every cereal as having an orange or red light rating.

There can be only one explanation. While osmium may be the densest material at surface pressures, at higher pressures many things can be more dense. As an example, consider a white dwarf star. A white dwarf is the burned out core of a star which has run out of hydrogen fuel and collapsed into a super dense state. Although calculating a diameter (and thus density) is not easy, they are generally thought to be about a million g/cc, or a ton/cc. On the Choice Magazine scale, that would weigh in at ten thousand 100g/cc.

Of course, white dwarfs are mostly carbon and oxygen, not sodium. But lets assume that they have a solar O/Na ratio. Using the Asplund et al. (2006) values, the solar O/Na ratio is about 300. But since white dwarves have carbon, silicon, etc. in them as well, we should really look at the ratio of everything except H and He to sodium. This is about 600 (in other words, carbon plus nitrogen plus all the heavier metals are about as abundant as oxygen).

So a white dwarf sodium content, using choice magazine units, is about 16.7 100g/mL.

Figure 1. The traffic light rating table from the choice magazine report.

That is more than ten times the 1.5 100g/mL “red light” value they suggest.

So eating degenerate matter from the cores of burned out stars is not recommended by Choice. It contains too much sodium, and might give you high blood pressure.

M. Asplund , N. Grevesse, A. J. Sauval; The solar chemical composition; Nuclear Physics A 777 1–4 (2006)

RIP Brian Welsh

Like many people who grew up in my hometown of West Windsor NJ, I was horrified that one of our West Windsor-Plainsboro High School teachers, Mr. Brian Welsh, committed suicide by train last weekend. Local newspaper reports can be found around the internet.

To say that Mr. Welsh was a great teacher is an understatement. He was a legend who made the Robin Williams character in “Dead Poets Society” look like a clock puncher.

When I was a student 20 years ago, Mr. Welsh taught a class on politics and law, called IPLE (Introduction to Political and Legal Experience). This is not a natural point of interest for teenage boys and girls. So the way in which Mr. Welsh sucked kids into his classes is something we could all learn from, even if few have the talent and passion to emulate the man.

The class was not required for anything, be it the district, the state, or any of the colleges to which students aspired. But it was a popular class, taken by everyone from the Ivy League aspirants to the kids on parole.

First, consider what he didn’t do. He didn’t sex his classes up. It was what it was, and there was no bait-and-switch or fancy dressing. He wasn’t a pushover; his classes appealed because they were involved, not breezy. He didn’t dumb it down. You had to work hard, write well, and get out and do all sorts of non-traditional activities. He didn’t hammer it in. There was no fear, or guilt, or condensation. The material was there to be learned by whoever was interested. Instead, Mr. Welsh motivated his students to learn.

I don’t know if I can really explain why he was such a great teacher. Certainly he knew his subject matter, and explained it passionately. His IPLE class requirements made it personal, though grading contracts, hands-on exercises and non-traditional requirements. I still remember a classmate of ours getting class credit for explaining his day in court where he beat a driving-with-suspended-license charge. Mr. Welsh used these features to connect what would normally be an austere, esoteric body of knowledge to our every day lives.

But most importantly, he gave the encouragement necessary to convince us kids that we could use this knowledge, and the applications of it, to make our way in the world. It isn’t that he showed us how to be lawyers or pundits; very few of us did (although those few have generally done quite well). The lesson was more fundamental than that. He inspired us how to combine our knowledge and our passions to set goals and achieve them. In that sense, the subject matter was irrelevant. Mr. Welsh taught us how to live.

Of course, the private lives of teachers are not necessarily obvious to their students, and I was certainly no less self-absorbed than your stereotypical teen-age knucklehead. I do remember the way that Mr. Welsh gushed about how amazing and heroic his wife was giving birth to their first child. But I couldn’t tell you what happened to him over the intervening 2 marriages and 20 years. All I can say is that of all the people I knew growing up, he was probably the last one I would expect to find on the tracks. That is what I find so heartbreaking.

Erratum

Please excuse me while I die from embarrassment, but I have had to append an erratum to my previous post. Whether this rises to the level of scientific misconduct is something that y'all can discuss amongst yourselves, but aside from the destruction of a major city in a nuclear fireball, the damage was pretty much contained. I might just go back to posting pictures (or nothing) for a while.

Tourmaline vs. the bomb

OK, loyal readers, it is Saturday night, and those of you without small children should be out watching action movies or something. If you aren’t lets pretend you are, just for this blog post. In the action movie that you aren’t watching right now, the heroine and her hippy dippy sidekick are trying to stop Islamic terrorists from detonating a home-made nuclear bomb on the Washington Mall, where it would damage the astounding geological collection of the Smithsonian*.

Our intrepid duo manages to break into the bomb inside the terrorist safe house, but they are unable to dismantle or remove it before they have to clear out. In a fit of desperation, our heroine yanks off the sidekicks hippy dippy tourmaline necklace, and lodges it between the subcritical spheres (terrorists don’t have the engineering savvy to build an implosion device), in hopes that the tourmaline will stop the neutrons.

As our intrepid duo makes a dash for their getaway combi, you all, being sensible nuclear geochemists, ask yourselves: Is that realistic, or crap?

Qualitatively, tourmaline contains structural boron, which is a decent neutron absorber. Using diamonds would have been crap, of course, but our sidekicks socio-economic and cultural background might have saved us there.

Fortunately, your movie theatre is equipped with envelope backs.

What is the relationship between the neutron capture cross sectional area of the boron and the crystallographic structure of the tourmaline? Let us look at the basics.

The simplest tourmaline compositional endmember is dravite: NaMg₃Al₆(BO₃)₃Si₆O₁₈(OH)₄ (don’t ask about the complicated ones).


Assume that the neutron capture cross section of everything except ¹⁰B is zero.

There are three formula units per unit cell, so that will be 9 boron atoms.

Boron is 19.9% ¹⁰B, so 9 x 0.199 = 1.791 ¹⁰B atoms per unit cell.

Great. How well does it stop neutrons?

The ¹⁰B neutron capture cross section is about 3825 barns.

What is a barn? 10^-28 square meters, or 10^-8 square angstroms.

So ignoring any overlap, our unit cell of tourmaline should have 3825 x 1.791= 6869 barns, 6.8x10^-25 square meters, or 6.8x10^-5 square angstroms. How big is the unit cell?

Since our envelope has access to webmineral.com, we can get the crystallographic information for trigonal dravite. And it turns out that the unit cell is 7.2 angstroms high, with an area of 220 angstroms. So the cross sectional area (per unit cell) of 6.8x10^-5 divided by 220 square angstroms gives us a ratio of 3.12x10^-7. Roughly speaking, that is the fractional change of the neutron being adsorbed per unit cell. One part in 32 million. It is not a very large number.

Luckily for us, though, our hippy dippy sidekick is not a Transmission Electron Microscopist, so his necklace is not thinned down to a few unit cells. Our 7.2 angstrom C axis means that a 1 mm length will have 1.39 million unit cells in it. Multiplying that by our chance per cell, we get 1.39x10⁶ x 3.12 x 10^-7 = 0.43. So 1 mm of tourmaline should block a bit less than half the neutrons.

A bit of internet shopping** says that a 50 buck pendant will be on the order of 10x40 mm, so it should actually be a fairly effective neutron shield. The bomb will fizzle, the world will be safe for geologists and hippies, and y’all can enjoy the rest of your weekend.

ERRATUM:
It has been pointed out to me that the thermal neutron capture cross section is not appropriate for fast neutrons that occur in a nuclear weapon (it's a bomb, so there is no time to slow the neutrons down to a nice speed). As a result, the effective cross section of boron in this situation would be much smaller (less than a barn), and there would be minimal fission inhibition. I apologize for vaporizing whomever was in DC last weekend.

But as we watch the mushroom cloud drift slowly across the Potomac, it is worth using this interlude as a teaching moment. The attraction of inter-disciplinary research is that applying techniques and approaches from an established subfield to other unrelated subfields can often result in rapid progress. However, one has to be careful, because as a newcomer to a particular subfield, there may be common traps or problems which which you are unaware. Left undetected, these can have catastrophic consequences.

* Disclaimer. I had a brief post-doc there.
** Note that in addition to the hippy dippy placebo effects, the online crystal monger does not mention that tourmalines are effective shielding against thermal neutrons. They don't know what they're missing.

The etiquette of reviewer suggestion

When submitting manuscripts to many journals, there is an opportunity to suggest reviewers for the manuscript. I have found that failure to do so can result in one or more reviews where the reviewer obviously had no idea what the heck was going on. However, as I have never suggested anyone as a reviewer, I’m not really sure how this works. Specifically, if one is to suggest a particular person as a reviewer, should one ask that person first? On the one hand, asking someone to review a paper is dobbing them in for a considerable amount of work, and asking for a review without prior contacts seems a bit like listing someone as a personal reference without asking. ON the other hand, the peer review system is supposed to be anonymous (you in the back, stop laughing), so in theory one could interpret potential reviewer solicitation as a breach of confidentiality. My gut feeling would be to ask people with whom I am comfortable corresponding, and to be very equivocal about putting any other names forward (e.g. Dr. X is knowledgeable in the field, but I have no idea whether he has the time or interest to review the paper). Any suggestions?

Laser pointer IR hazard

There is a recent technical note from NIST out describing potential IR hazards from off-the-shelf green laser pointers. It makes use of the CD spectrometer that I blogged about years ago, but is far more quantitative. It also shows a cool trick for detecting IR leakage from household lasers: evidently cheap webcams can see IR, while good digital cameras do not, so the images can be compared, to detect IR.

More importantly, I think it is awesome that the federal government is encouraging people to set up physics experiments at home using paper cups, old music, and other stuff lying around the house. Take that, lawyers and stuffy nay-sayers!
The technical note, "A green laser pointer hazard" is here.
The experimental setup is shown below:


And a comparison of visual-only and visual+infrared diffraction image is below. The bright white dots are 808 nm IR leakage from the laser. This constitutes an eye hazard.

Cordierite

Cordierite is a high temperature metamorphic magnesium-aluminosilicate. It is interesting because it contains no water in its structure, but contains large channels (see picture) into which water will readily bind, with up to about 1.2 H₂O per formula unit (Mg₂Al₄Si₅O₁₈). Unlike most non-structural water, cordierite can hold onto water in this site under very high temperature conditions, such as granulite facies metamorphism.

Because the water is not bound to a specific site, it has high entropy for a non-vapor phase, which of course explains the high temperature stability. It also leads to some funky phase transitions.

Nicest reply to critical comment ever...

is from Shao-Yong Jiang, Geochemical Journal 40, 639-641, 2006. (.pdf link)

From his conclusion:

Erroneous data with extremely low δ11B values were obtained during analysis of tourmaline from Lavicky granite and Altay pegmatite using an acid digestion technique and TIMS measurements. We thank Marschall and Ludwig for pointing out these problems.

I've read a few comment-and-replies in my time, and I don't think I've seen an author ever thank the commenter for catching a mistake in the original paper before. The best one can generally hope for is mealymouthed mutterings about the difficulties of reproducibility, or grudging retraction. Can someone please give Dr. Jiang a civility award? And forgive his use of the royal "We".

Blogging here is continuous on geologic timescales

But those of you looking for subannual periodicity may be disappointed. I'm trying to finish a paper and progress has been slow. Do any of you parents or other obligatory multitaskers have useful strategies for keeping track of manuscript progress when available time is split up into 10-30 minute segments? I'm finding that by the time I figure out where I was up to the last time I was writing, the boy has thrown up on the carpet and the girl's run naked into the front yard, and writing time is over. I'm suffering from too much punctuation, and not enough equilibrium. Any tips?

p.s. The boy only sleeps 10 to 5:30, so getting up early only gives a small window.

Is it wrong...

To cobble together a 40 page manuscript that doesn't quite make sense, submit it to a journal under a false name and address, and recommend 3 people you really don't like to be the reviewers?

A different take on the PepSciBlog scandal

Much has been said of the PepSciBlog scandal, both by PepSciblings, the MSM, and the rest of the internet. I won’t repeat or comment on any of those opinions. Instead, I will try to prove that corporate shilling can be useful to basic science education, by using the Pepsi logo to explain the Rossiter-McLaughlin effect. Steinn should be ashamed that he didn’t beat me to this.

Imagine that in the days before spin, the Pepsi logo was designed by physicists, and thus was a featureless, luminous white sphere.


Figure 1. The pre-spin Pepsi logo.

This is fine for the Precambrian, but here in the 21st century, spin is very important. So we will spin the logo.


Figure 2. The spinning logo.

Spinning the sphere means that the side spinning away from us will be red shifted by the Doppler effect, while the side spinning toward us will be blue shifted. This is well illustrated by the modern logo.

This is fine, as long as the Pepsi logo spins alone, in the vastness of space. But interactions with other logos are important. Consider, for example, a transit, or partial eclipse, of the Pepsi logo by the Diabetes Australia logo.


Figure 3. Beginning of a diabetes transit of Pepsi.

If the direction of the transiting logo is the same as the direction of spin from the pepsi logo, then the light from the blue-shifted portion of the logo is blocked first. This makes the average observed Pepsi light somewhat redder. Later, as the Diabetes Australia logo moves to block the red-shifted part of Pepsi, the average light becomes bluer.


Figure 4. Late stage of a Diabetes Australia transit of Pepsi.

Like our hypothetical pre-spin Pepsi logo, stars are (approximately) luminous white spheres. So if they are rotating, the same effect can be observed when planets transit in front of them. More details of this effect can be found at the systemic blog. Thus education triumphs (until the evil lawyers shut me down).

Update:
A former Frink Tanker tells his story.

Goldschmidt paleoblogging- the schmooze

Of course, one of the attractions of conferences, aside from the hot science and the big deals and the free* beer, is meeting the people whose papers I read, and catching up with colleagues and friends. And the conference did not disappoint in this regard either. I met a wide variety of ion probers, most of whom were friendly and smart. And I was pleasantly surprised at the number of people who I hadn’t seen in over a decade, who wandered up to me at some point and said g’day**. I saw people from Brown, people from field camp, people from grad school, and people from my technician days back at RSES. And many of the people, especially those who I hadn’t seen in ages, were doing awesome science. And if that wasn’t enough, I had the smallest possible geoblogger meetup (n=2) with petrological skepchick Evelyn, who is as enthusiastic and friendly in real life as she is on the internets.

So overall, it was a surprisingly fine meeting, not withstanding any overexertion on the part of my liver or my brain. They should both detox on the plane, which would be good since I miss my kids and wanna have a hangover-free play when I get home.

* excluding the conference fees, of course.
** or howdy or hello or whatever it is that they say in east Tennessee

2010 minimum arctic sea ice betting pool

Update 2!!
I think this is it, unless Eli and GFW and crandles wish ti reguess for reasons stated in the comments.

Update! The guesses so far are posted below. Contest will close tomorrow night once I get the kids to bed and clean up- call it 30ish hours from now. We're all a bunch of doom-glooming alarmists so far!

original post

The 2010 Arctic sea ice extent minimum prediction pool is now open.

Guesses are to be in the form of extent and sigma (a mathematical measure of uncertainty), in thousands of km² You may use decimal places if you insist.

Your guess will define a Gaussian curve.

The function with the highest value for x=minimum daily measured ice extent (from IARC-JAXA) wins.

See the 2009 announcement, opening, and final curve for details.

I apologize for not posting on the solstice, but I was in transit from a conference in America.

This contest will close much sooner than last year's. Guesses must be submitted by the time the Earth reaches aphelion in its orbit, which the internet tells me is 11 am on July 6 (presumably UTC). Trash talking, dissembling, and boasting in the comments section is encouraged.


Figure 1. Last year's contestant curves and final 2009 minimum sea ice extent (red line).

As with last year, the winner gets to pick a topic for a silly blog post.

More on the asbestos dust-up

Silver Fox has an excellent summary of serpentine group minerals, serpentinite rock, and the various asbestiform minerals. An even more interesting discussion has taken place on the pages of Elements magazine, the joint membership / review journal of a number of mineralogical and geochemical societies.

In June 2009, Micky Gunter wrote a scathing article on how mineralogists were being left out of the asbestos debate. This was complimented by an outreach article by Thomas Feininger on the use of Mg₃Si₂O₅(OH)₄ as the launching pad for all sorts of cool interdisciplinary and instructional mineralogy.

Four months later, Gregory Meeker of the USGS chimed in on the dark side of mineralogists in the asbestos debate, and Micky Gunter replied. The following part of Meeker’s article is worth quoting:

Gunter takes exception to a recent legal definition of asbestos; but there is more to that story. For over 70 years, the fibrous amphibole that is a major—not trace—constituent in the Vermiculite Mountain vermiculite deposit near Libby, Montana, was called tremolite, sodium-rich tremolite, or sodic tremolite by everyone including the mineralogists and geologists who studied the deposit. During the 1970s, the names of the regulated asbestos minerals, including tremolite asbestos, were entered into the U.S. Code of Federal Regulations. As recent court proceedings have revealed, company geologists, owners, and operators of the vermiculite mine near Libby understood that the asbestiform amphiboles in the mine fell under those regulations. In 1978 and 1997, committees of the International Mineralogical Association published new recommendations for amphibole nomenclature. Based on this new system of nomenclature, most of the amphibole minerals at the Libby mine were reclassified as winchite. When public and regulatory attention returned to Libby in 1999, mineralogists working on behalf of the company that owned the mine used the changes in nomenclature to claim that the majority of the Libby amphibole had been mistakenly identified as tremolite and therefore was not regulated. A federal judge sided with the defense and, based on a 2003 USGS study of the minerals, ruled that only 6 percent of the Libby asbestos was regulated.

In short, the mining company mineralogists and lawyers knew perfectly well that their waste was just as deadly as ever, but they used a name change as a loophole to avoid culpability.

I originally came across this story with the intention of using it of an example of why nomenclature and other definition committees should not be too high-minded and ivory tower- in this case, the amphibole reclassification let the bad guys get away with murder. And this brings us to the comment section of the California bill:

Chrysotile serpentine, also known as white asbestos, is the most common form of asbestos. Mg₃(Si₂O₅)(OH)₄.

Putting the idealized serpentine group formula in a sentence all by itself is extremely nebulous, but one way of reading this is that they are trying to define asbestos as Mg₃(Si₂O₅)(OH)₄. This would, of course, exclude the dangerous asbestiform amphiboles (e.g. Na₂(Fe,Mg)₅Si₈O₂₂(OH)₂, or crocidolite) from the definition. This strikes me as asking for trouble.

Further reading:

Ann G. Wylie and Jennifer R. Verkouteren; Amphibole asbestos from Libby, Montana: Aspects of nomenclature; American Mineralogist; October 2000; v. 85; no. 10; p. 1540-1542

The Composition and Morphology of Amphiboles from the Rainy Creek Complex, Near Libby, Montana; G.P. Meeker, A.M. Bern, I.K. Brownfield, H.A. Lowers, S.J. Sutley, T.M. Hoefen and J.S. Vance; American Mineralogist; November-December 2003; v. 88; no. 11-12; p. 1955-1969

Mickey E. Gunter, M. Darby Dyar, Brendan Twamley, Franklin F. Foit, Jr. and Scott Cornelius; Composition, Fe3+/{sum}Fe, and crystal structure of non-asbestiform and asbestiform amphiboles from Libby, Montana, U.S.A.; American Mineralogist; November-December 2003; v. 88; no. 11-12; p. 1970-1978.

Mickey E. Gunter, Karen E. Harris, Kristin L. Bunker, Rebecca K. Wyss and Richard J. Lee; Amphiboles between the sheets: observations of interesting morphologies by TEM and FESEM; European Journal of Mineralogy; December 2008; v. 20; no. 6; p. 1035-1041; DOI: 10.1127/0935-1221/2008/0020-1872

Mickey E. Gunter, and Matthew S. Sanchez; Amphibole forensics: Using the composition of amphiboles to determine their source, the Libby, Montana, example; American Mineralogist; May-June 2009; v. 94; no. 5-6; p. 837-840; DOI: 10.2138/am.2009.3224

In defense of serpentine

There is a move by asbestos activists and litigators in California to remove the status of state rock from serpentine. The language of the bill is heavy on the health effects of asbestos, particularly amphibole asbestos (which has no relation to serpentine at all). It makes some completely inaccurate statements, such as the allegation that all serpentines contain asbestos. It downplays, or completely ignores several of the key benefits of serpentine. So, three simple reasons why serpentine is great:

1. Serpentine sequesters CO₂. Under atmospheric conditions, serpentine reacts with carbon dioxide in the air to form magnesite + quartz + water, via numerous intermediate hydrous magnesium carbonates. Mineral carbonation of serpentine is one of the most promising methods of removing CO₂ from the atmosphere.
2. Serpentine prevents earthquakes. In central California, the portion of the San Andreas fault that cuts through serpentine bedrock does not suffer from catastrophic earthquakes. Instead it slowly and peacefully creeps. The 1989 Loma Prieta earthquake, which killed 63 people, could have been as big as the 1906 San Francisco Earthquake, which killed more than 3000 people, were it not for the presence of serpentine (and alteration products) in the fault to the south of the rupture area.
3. Serpentine may be responsible for life on Earth. The formation of serpentine from the reaction between water and the Earth’s mantle releases hydrogen gas, which combines with CO₂ to form methane and organic molecules. This hydrogen is a food source for methanogens, one of the Earth’s most primitive and ancient life forms, and the unusual chemistry associated with serpentine formation could well have provided the building blocks and energy source for the birth of all of life on earth, including the California state legislature.

In short:
There are 20 forms of serpentine, only one of which is an asbestos mineral.
The very dangerous amphibole asbestos minerals specifically mentioned in the bill are completely unrelated to serpentine.


Safety disclaimer: The inhalation of ANY rock dust is harmful to the lungs. Asbestos dust is particularly dangerous. Do not breathe rock dust.

Detrital minerals done right

This afternoon, I got to go listen to a talk by Andy Morton. As anyone who hangs around the geochronology scene for any length of time knows, detrital provenance studies are done often, with a wide variety of quality and rigour. The basic idea is that you can learn about the source region of a sand by looking at the individual grains. How much you learn, and what sort of study is most informative, is something that isn’t always clear, as this is a field of study where the wheel is reinvented often and badly. The basic idea is so simple that people don’t often spend oodles of library time looking at how the field has evolved over the decades. So it was really cool to listen to the guy who has been at the forefront of doing detrital studies well for the last 30 years.
Like much great science, the talk was deceptively simple. He started out explaining the various sedimentary processes that give rise to sample bias, specifically diagenesis, transport, and weathering. He then went through the heavy mineral ratios, and the chemistry of each one- what the garnet chemistry tells you, what the tourmaline chemistry means, etc., through the entire mineral suite. Only after that did he get into geochronology. And each piece of the puzzle fell together- the tourmalines identified the granite types, the rutiles identified the high grade metamorphic conditions, the garnets identified the medium grade metapelites and deep crustal rocks, the zircons gave the ages. Occasionally spinels would make mafic igneous cameos. As it came together, the picture of the source would suddenly congeal- Of course that combination of X metamorphism and Y plutonism at time Z was from source region W- once all the pieces are assembled, it’s perfectly clear.
And once the provenance is determined, the alteration overprint on the source assemblage in various sands of similar derivation can be used to determine burial temperature, source weathering, flood plain behavior, and a host of other paleoprocesses that most detrital mineral amateurs don’t even begin to consider. It was awesome.