Sunday, October 31, 2010

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.

Monday, October 25, 2010

Meteorite tea, and the failures of genius

ResearchBlogging.orgIn 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

Saturday, October 16, 2010

Saturday, October 09, 2010

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.

Wednesday, October 06, 2010

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.