Monday, September 29, 2008

Accretionary wedge and more

Geology in space, the 13th repeat of the Accretionary wedge, is up at goodschist. In addition, has a large collection of geoblogs listed. So go read their stuff.

How to arm Bridezilla

A couple of years ago, (which is an epoch on blog timescales), Jen over a cocktail party physics blogged about diamonds, gold, and other constituent materials of engagement rings. Since I did my PhD on diamonds, we had a bit of a discussion on the subject. Not long afterwards, her cat evidently lost said ring, generating predictable distress.

Since Jen is a journalist, and Sean is a theoretician, I planned a blog entry describing a variety of non-destructive analytical techniques which they could use to find said article of jewelry. This way, should one of them go Bridezilla (or Groomzilla), they would have a variety of caustic, ionizing, and nuclear tools at their disposal. Unfortunately, said post languished in my half baked finished box for the better part of a Wilson cycle. However, as today is their wedding anniversary, I figured I might excavate it, dust it off, and post. So without further ado:

Engaging ways of finding a ring

The following analytical techniques are standard geochemical techniques that have been used to analyse diamond and/or gold by various scientists over the years. Destructive techniques, though generally more effective, have been excluded from this list. Each method consists of a short description of how it works, and summary of the experimental setup you will need, and a brief description of what the side effects might be for the cat. They are listed in increasing order of impracticality.

Xray induced optical fluorescence

Theory: Most diamonds fluoresce in the optical wavelengths when illuminated by X-rays, as a result of impurities and structural defects. In fact, this technique is usually what is used to recover the diamonds from the kimberlite ore in the first place. The ground ore is illuminated with X-rays, and anything that glows is retrieved (all in a highly automated process).

Method: Black out apartment. Irradiate everything in it with X-rays. Grab anything that glows.

Effect on cat: increased cancer risk from moderate X-ray dosage.

X-Ray fluorescence

High energy X-rays will knock inner shell electrons out of the atom. When outer shell electrons fall down to fill the vacant shell, an X-ray is emitted. These X-rays can be detected with an X-ray spectrometer, which will identify the element being irradiated. Since most apartments don’t have a lot of gold lying around, looking for Au K , L, and M band X-rays will detect the gold instead of the diamond. Better yet, the K and L X-rays are quite energetic, so if the ring is obscured by a low Z number object (like a cat), they may be able to penetrate it.

Method: as above, but with a high energy, brighter source (Is there a synchrotron in your block of flats?).

Effect on cat: Chronic radiation damage, but with a higher dose.

Gravimetric/ magnetic separation

Theory: Diamonds and gold are both denser than wood, plastic, concrete, and most other building and furnishing materials. Unlike steel, they are not ferromagnetic. So a gravimetric and magnetic separation should reveal the ring.

Method: grind apartment into gravel-sized bits. Use a magnet to pull out any steel. Dump the remains in a heavy liquid (a variety of iodine or bromine organic molecules are available for this purpose) which will float the concrete (as well as plastics and wood) Your ring should sink and be recoverable.

Effect on cat: The grinding step may produce physical damage. In addition, most heavy liquids are extremely toxic.

Acid dissolution

Theory: diamond and gold are both very insoluble in most caustic liquids. Dissolving the apartment with increasingly aggressive solvents should leave the ring untouched.

Method: dissolve plastics in the appropriate organic solvents. Dissolve wood in this stuff. Dissolve concrete, ferrous, and base metals in sulphuric acid.

Effect on cat: Ends up in a solution of the fairly final variety.

Mössbauer Spectrometry

Theory:197Au, the only stable isotope of gold, has an excited isomer which decays back into the stable isotope with a half life of 7 seconds. By irradiating stable gold with gamma radiation of the exact energy required (about 400 KeV), a nuclear transition to the excited state can be induced. This will then decay with the same characteristic energy, which can be detected with a gamma ray spectrometer.

Method: Irradiate the flat with gamma rays of the appropriate energy to excite the Au nucleus. Then switch on your GRS and home in on the emitter.

Effect on cat: Gamma ray irradiation is similar to X-ray damage described above, but potentially more penetrating.


Theory: Proton-Induced X-ray Emission. This is similar to XRF, except that high energy protons are used instead of X-rays. The disadvantage is that you need a particle accelerator- nothing LHC sized,as a few MeV is the energy most commonly used. The advantage is that proton beams can be focused better than X-rays, allowing you to target your search more carefully.

Method: Remove an elevator and install a particle accelerator in shaft. Evacuate apartment. Raster beam across all potential hiding places, and use an X-ray detector to spot emission from inner shell ejection of electrons from the gold atoms.

Effect on cat: death by asphyxiation. Potential additional radiation damage from proton beam.

Neutron activation

Theory: 197Au will fairly easily absorb a neutron, transforming to the radioactive isotope 198Au. This isotope decays so 198Hg with a half-life of a couple of days, releasing a characteristic gamma ray in the process. Both neutrons and gamma rays can easily penetrate all but the best shielded of hiding places, making this method ideal. Note that only a tiny fraction of the gold atoms are transmuted, so the mercury toxicity threat and loss of gold from the ring are both minimal.

Method: Construct an unshielded nuclear pile in your living room. Flood flat with neutrons. Afterwards, send in a radiation-shielded robot with a gamma ray spectrometer to detect 198Au decays. The apartment (and most of the building) will be uninhabitable for a few decades due to the production of radioactive elements, but the ring will only be too hot to handle for a month or so.

Effect on Cat: Death from acute radiation poisoning.

So there you have it. Jen, Sean: Happy anniversary. And just remember, if you ever need to find anything, science is always on your side.

Saturday, September 27, 2008

Carnival of space #72

Is live over at twisted physics.

Thursday, September 25, 2008

Always use pencil

Write-in-the-rain notebooks are of dubious utility when used with water soluble ink...

Of course, waterproof ink in not necessarily a good defense. When I was a student, I once had a technician use my lab book to smother an ethanol fire. The fire went out, and the notebook even soaked up the residue, neatly removing the hazard. Trouble is, there aren’t many inks that aren’t soluble in ethanol. While the chromatography patterns were awesome, reconstructing my work for the past month was a bit of an effort. The nice thing about graphite is that it is insoluble in anything that doesn’t attack paper.

Tuesday, September 23, 2008

The Earth Science President

Which Presidential candidate is best for Earth scientists? I’ll briefly have a look at some issues, then let y’all discuss. Please note that this is an autopost that I actually types up 2 weeks ago; so if something interesting happened since the Republican convention, it will not be considered.

Issue one- Resource extraction.
The Republicans seem to be considerably more gung-ho about exploring for and developing mineral and energy resources. The Democrats are considerably less enthusiastic about domestic fossil fuel production. In addition, Palin strongly supported infrastructure projects like pipelines which are crucial for developing small and medium sized deposits.
McCain wins this category.

Issue two- Regulation
Good regulation can actually benefit Earth scientists. While mining certainly employs geoscientists, reclamation, remediation, and water monitoring also provide good jobs for us, provided the regulatory environment creates a need for their skills. On the other hand, bad regulation can stop a project from progressing at all, or provoke a company into hiring lawyers to fight the regulations, instead of using earth scientists to follow them. I suspect that the Democrats would impose more stringent regulations, but I don’t see the evidence that their regulatory regime would be constroctive, rather than obstructive.
McCain wins again

Issue three- Education and research
Obama has promised substantial increases in federal funding for schools, college students, and research funding. While it is not clear if his research funding increases would proportionally increase Earth sciences relative to other fields, I suspect that there would be at least some improvement. In contract, the Republicans promise mostly to cut “wasteful” spending. In addition, the Republican VP is on record opposing evolution in schools. Since evolution is important keystone of geology, I can see a situation where the Republicans authorize drilling for everywhere, only to find that there are not enough qualified geologists around to site the holes.
Obama wins this one.

Issue four- Economy
The current high prices for most mineral resources is a direct consequence of rapid economic development in Asia, principally China and India. In recent months, there have been signs that the deteriorating US economic position is starting to effect growth all over the world. So strong US leadership is useful for maintaining worldwide growth to support prices. The Republican economic plan doesn’t seem particularly sound, as it continues expensive tax cuts and military programs without any obvious spending cuts of similar magnitude. While the democrats have a large number of spending proposals, I feel that their overall economic vision and ability is probably stronger.
Obama wins again.
If anyone can think of a tiebreaker issue, post it in comments. Please frame all comments as what is best for geology and its practitioners, however. While I acknowledge that people may vote for reasons unrelated to their profession, there are about a billion other blogs that are discussing that issue already.

Saturday, September 20, 2008

I’d like to thank the alaskademy

It looks like the generous allochthonous Alaskan who blogs as Wayfarer Scientista has given me the Brilliante award. Presumably, this is some sort of baddeleyite allotrope.

Baddeleyite, formula unit ZrO2, is a great mineral, so it is a shame that synthetic cubic zirconia has a higher profile in the more colorful parts of non-geologic human culture. Of course, the trick to getting ZrO2 to grow in a cubic structure is itself interesting- it seems that cubic zirconia is in fact a Zr-rich tazheranite solid solution. But growing big crystals at all is impressive when you consider that zirconia has one of the highest melting points of any known substance. But enough of this lapidarial digression.

In order to crystallize baddeleyite, two conditions must be met. Firstly, the major minerals must be saturated in Zr. Secondly, the SiO2 activity has to be low enough that zircon doesn’t grow. This makes the mineral somewhat uncommon. Never the less, it does have a high U/Pb ratio, so it is used for geochronology for rocks that don’t have zircon.

Interestingly, metamorphic fluids are often silica rich, so in some altered rocks a zircon reaction rim will grow on a baddeleyite, allowing both the crystallization age and the alteration age to be determined. In practical terms, this means that if you want a good date, then natural, monoclinic zirconia is more reliable than its artificial, cubic allotrope.

Evidently I am supposed to pass this award along, so nominate the following blogs as being cubic zirconia-worthy:
The Planetary Society Blog
Molecule of the Day
This non-American Life
Apparent Dip
The Volcanism blog
All my faults are stress related
And if any of y'all have already been awarded, then give yourselves an allotrope instead.

Tuesday, September 16, 2008

Isotope Park

When it comes to extinctions, animals are extremely over-represented in the public eye. Everybody knows what a dinosaur is. And most people have heard of trilobites. But seed ferns? Not so much. And when it comes to nuclides, the lack of public recognition is even more severe. When’s the last time your non-geological friends told you their 6 year old loves 60Fe?

I would like to correct this. Extinct nuclides are vital to our understanding of the solar system, and are every bit as deserving of popularity as a triceratops. I consider this to be an injustice, a disgrace. I will not be satisfied until Hollywood blockbusters have Laura Dern fleeing in terror, as a pack of angry- and radioactive- molecules of 26Al129I3 come chasing in pursuit.

But before this dream can become a reality, I should probably explain what they are.

Extinct nuclides are radioactive isotopes that no longer exist in detectable quantities in the modern solar system, but whose presence in the early solar system can be deduced from their decay products. A table showing several geologically interesting live and extinct isotopes is shown below, with a logarithmic timescale at top.

Extinct nuclides are valuable for establishing timelines for the first 1-50 million years of the solar system’s history. This is the time during which the protoplanetary disk cools enough to start condensing crystalline matter, and this matter then forms condrules, asteroids, planetesimals, and eventually, the terrestrial planets that we know and love today. It is constrains from these isotopic systems that tell us the chondrites and apparent bodies for iron meteorites formed in the first few million years, while the time required for these planetesimals to collide and form the four inner planets was about ten times as long. This is all a result of painstaking isotopic analysis and interpretation using a fairly simple theory. The story goes like this:

Once upon a time, there was a giant molecular cloud. One day, a nearby star exploded in a supernova. This supernova created lots of R-process and P-process nuclides, including all the short lived ones. The shockwave triggered a collapse of the molecular cloud, and initiated the formation of the sun and the rest of the solar system, with all these newly formed nuclides mixed in. The radioactive ones decayed, but the stable ones lived happily ever after.

At least, that’s what we geochemists thought. Unfortunately for us, a gang of tactless astrophysicists crashed our storytime party and spewed numerical garbage all over our tidy white cleanrooms. But that is a discussion for another day.

Friday, September 12, 2008

Love and loss at one and a quarter

Look daddy!

A balloon!

Watch me practice sitting...

I am so proud that she didn't cry.

Tuesday, September 09, 2008

Fifty great minerals

For the last 34 million years, the “50 great books” meme has been polluting the otherwise focused blogosphere. More recently, knockoffs such as the top 7.5x101 - 103 popular science books, or the top foods list have been appearing. As a geologist I am mortified that such frivolities should appear when there are much more important things to put in fanciful-yet-judgmental bandwagon lists. I mean, let’s be honest here. Books and food comprise a volumetrically insignificant part of this planet’s mass. If we want to list something substantial, we should to isotopes. Or rocks. Or minerals.

So without further ado, here is the list of 50 minerals that everyone should see.
Use bold to indicate minerals you’ve seen in the wild. Italics is for those seen in laboratories, museums, stores, or other non field locations. Ex pet nerds may use underlining to indicate those that they’ve grown with their own two hands. And I won’t bother with stuff you intend on seeing- if you didn’t want to see all these minerals yourself, you’d be spending your precious lunch hour on a physics or biomedical blog.

50 minerals everyone should see:
Silver (native)
Sulphur (native)

Saturday, September 06, 2008

Carnival of Space 59

This week, the carnival is an alphabetical rhyme.

Wednesday, September 03, 2008

Culturally sensitive sexism

In these days of reconciliation, it seems that being a sexist prick is no longer exclusively the privilege of crusty old white guys. According to the news this morning, aboriginal academics are calling for a book to be pulped because it encourages girls to play the didgeridoo. Says Mark Rose, general manager of the Victorian Aboriginal Education Association:

"I reckon it's the equivalent of encouraging someone to play with razor blades. I would say pulp it."

Tuesday, September 02, 2008

The Inner Solar System

The stellar system hosting this blog is characterized by two gas giants and two ice giants. These four bodies constitute 99.5% of the planetary mass of the system. However, there is a small amount of rocky matter orbiting close to the star Sol, which accreted in an area too warm for the ices to condense into proper sized planets. Although this part of the solar system is dynamically insignificant, great importance is placed on it by a particular species of bipedal mammal, as these creatures are unfortunate enough to live on the largest of these rocks. In the following picture, all three other planets and the planet-sized moon of the largest object can be seen behind the clouds of this largest inner planet’s atmosphere. Readers interested in the relative mass of these planets are referred to the rocky planet pie chart. Correct identification of each rock is left as an exercise for the reader.