Saturday, August 29, 2009

New definitions from the International Astronomy Union

Last month, the IAU got together for their first meeting since the redefinition of Pluto that some of us predicted: And sure enough, there are more definitions.

The nations of the world now only include the G8- Canada, France, Germany, Italy, Japan, Russia, United Kingdom, and United States. All other countries have been redesignated as ‘dwarf nations’ to reduce the burden of memorization on school children.

Although it was an international astronomy meeting, the USA was formally reduced to five states: Hawaii, California, Arizona, New Mexico, and Texas. Those former states and territories whose observatories do not host at least one telescope with a 3 meter primary mirror have been relegated to the amateur anonymous land category. The union felt very strongly that reducing the trauma caused by the memorization of state capitals justified this change.

And finally, the periodic table of the elements has been redefined. Instead of 112 elements stretching from hydrogen to copernicium, astronomers will recognize only hydrogen and helium, relegating everything else to the category of ‘metals’, irrespective of the behavior of the electron shell.

Friday, August 28, 2009

Carbonado cathodoluminescence challenges

ResearchBlogging.org
When I was a PhD student, I published a short paper in the Proceedings of the VIIth International Kimberlite Conference on luminescence from radiation-induced crystallographic defects in carbonado, a type of polycrystalline diamond. Being a proceedings paper, it was short format- 4 pages, and 6 figures. This work found its way into my Thesis, of course. But since the structural and stylistic conventions of a PhD thesis differ from that of a conference proceedings, that version was 49 pages and 34 figures. After graduating, I tried to publish a condensed version of the full work, but I couldn’t get it accepted anywhere- the conclusions were no different than the short version that came out in ’99, so it was considered uninteresting, old news, and beating a dead horse. I gave up submitting it sometime in 2003 or so.

Fast forward to last year. Yokochi et al. (2008) publish a lovely paper of carbonado spectrometry and microtexture. Their photomicrographs are probably the best published to date. They see the same spectrographic peaks and textural features that have been known since Fettke & Sturges (1933). And with the addition of some nice stable isotope and argon work, they find a novel way to put it all together.

Figure 1: Yokochi et al.'s figure 1b, showing euhedral phenocrysts in a bright matrix. I reckon the CL-dark areas in the upper left of the figure are probably from epigenetic radiation damage. Evidently he prefers another explanation.

In the process of interpreting their fabulous images, they say:

These circular textures are analogous to CL images of carbonado from Central Africa in previous studies (Magee & Taylor 1999, Kagi et al. 2007). Although these authors interpreted them as a result of radiation damage, our cathodoluminescence images show no link between the circular texture and the pores in which the radioactive elements might have been resided. Moreover, the size of this circular texture is occasionally larger than the range of a-particle influence (20 ┬Ám). An alternative hypothesis for this particular sample may be that this circular texture had first formed as phenocrysts at earlier stage, and the rounded shape and vague boundaries imply either a partial dissolution of the phenocrysts prior to the formation of the flow structure or an annealing that has erased the sharp boundary after a discontinuous growth.
Now, I don’t think their interpretation is correct. In fact, I have a highly detailed case to support our original interpretation- which is that grain-boundary-crossing CL quench features are epigenetic in origin. But it has been sitting in the back of my garage since we bought the house because nobody has ever doubted the short&sweet version before. Hopefully, the emergence of an alternative hypothesis will make the longer argument relevant.

So, if I’m not blogging here, it means that I’m trying to track down co-authors from a dozen years ago in order to get this paper submitted. Or it means my daughter’s sick. Or the garden needs attention. Or I’m wasting time on facebook instead of wasting time blogging.

Just like carbonado cathodoluminescence features, there are not several competing hypotheses for light blogging here at the lounge.

Refs:
Fettke, C.R., and Sturges, F.C., 1933, Structure of carbonado or black diamond: American Mineralogist, v. 18, p. 172-174.
Kagi, H., Sato, S., Akagi, T., and Kanda, H., 2007, Generation history of carbonado inferred from photoluminescence spectra, cathodoluminescence imaging, and carbon-isotopic composition. American Mineralogist, Volume 92, pages 217-224.
Magee, C.W. & Taylor , W.R. (1999): Constraints from luminescence on the history and origin of carbonado. Int. Kimberlite Conf., 529-532.
Magee, C. W. 2001. Geologic, microstructural, and spectroscopic constraints on the origin and history of carbonado diamond. Ph.D. Thesis, Australian National University.
Yokochi, R, Ohnenstetter, D., Sano, Y., 2008, Intragrain variation in d13C and nitrogen concentration associated with textural heterogeneities of carbonado. The Canadian Mineralogist Vol. 46, pp. 1283-1296.

Yokochi, R., Ohnenstetter, D., & Sano, Y. (2008). INTRAGRAIN VARIATION IN 13C AND NITROGEN CONCENTRATION ASSOCIATED WITH TEXTURAL HETEROGENEITIES OF CARBONADO The Canadian Mineralogist, 46 (5), 1283-1296 DOI: 10.3749/canmin.46.5.1283

Wednesday, August 26, 2009

Why investors need stoichiometry

I was browsing the internet recently, eyeballing some of the ASX releases of various other exploration companies working in the NT, when I noticed the following release (pdf).

The headline announcement is “MgO values of up to 37.9% after removing LOI.”

A brief aside:
Magnesium is commonly mined from magnesite, MgCO3, and a brief description of several mine types can be found here (pdf). Magnesite decarbonates at a few hundered degrees C to MgO + CO2. As shown in the article above, ore grades are often reported as %MgO after LOI (so pure magnesite would be 100%).

Magnesium is a very common element, though, and is found in all sorts of other less economic minerals, such as pyroxenes, dolomite, hornblende, talc, etc. But it is generally less economical to extract Mg from these minerals. If, as this AXS release suggests, their exploration model is a Kunwarara-type sedimentary magnesite deposit, then they may want to demonstrate that their magnesium is actually in magnesite, and not some other less economically useful mineral.

So I wondered, is the magnesium content of dolomite after LOI greater or less than 37.9%? Dolomite, CaMg(CO3)2, decomposes to CaO + MgO+2CO2, which is lost. Using masses of 15.9994 for O, 24.3050 for Mg, and 40.078 for Ca (via webelements), we get a LOI-removed MgO content of 41.8%. So any bulk analysis greater than this amount must contain some phase that is more MgO rich than dolomite (like magnesite, the stuff we are looking for).

Trouble is, their highest reported value is 37.9% MgO, from what they describe as “dolomite nodules”. Assuming no other Mg bearing minerals, 38% MgO corresponds to a rock that is about 90% dolomite. Now, finding dolomite could be very exciting in some parts of the world where carbonates and magnesium are rare. But the Georgina basin is full of dolostone.

Of course, if there is no calcium in the rock, then their can't be any dolomite, and it could very well contain magnesite. We don’t know what the other 68% of the rock is made of. But given that they report dolomite nodules, and dolomite has a higher post-LOI MgO content than what they found, there is no reason to believe that they have any magnesite.

Read this part carefully:
I am not an investment advisor. Anyone who buys or sells shares based on my advice will probably end up broke. But I am a geochemist. And based on the calculations above, these reported results are consistent with having found a common rock type in the Georgina Basin, and not magnesite.

Monday, August 24, 2009

Banning powerpoint is not enough

Recently, Kim suggested that an SMU dean was not acting correctly by banning technology from the classroom. I’d like to back this dean. In fact, I don’t think he goes far enough.

Powerpoint, podcasts, and filmstrips are just the tip of the Cryogenian iceberg here. If we really want to get back to teaching old-school, there is an equally pernicious development that has to be addressed before a classroom can be truly free of newfangled gimmicks. We need to ban chalk.

Forget about all the arguments over allergies, unfashionable smudges, and unacceptable strontium blanks. The real problem with chalk is that it is too new. How can the effects- and dangers- of a teaching technology be fully appreciated for a device that is a mere 0.07 gigayears old? When I was a kid, those slate blackboards weren’t even slate yet, and the Cretaceous was just a twinkle in a basal therapod’s eye.

Now, I am not a lubbite. I had no complaints about the moon-forming impact, the emergence of continents from the primeval sea, or even plate tectonics revolution. And I’m coming around on this whole oxygenated atmosphere thing. But chalk? Let’s be honest here, folks. For 85% of the Earth’s history, there were no fossils, much less undeformed diagenetically unaltered ones. Cemented coccoliths have no place in the 21st century classroom.

Thursday, August 13, 2009

Phase diagram question

What do you guys use to plot ternary phase diagrams?

Does it run on a PC?

Is it Excel-compatible?

Does it do 3-D (4 component) systems?

Does it correctly plot error ellipses?

If the answer to all those is yes, please let me know.

Saturday, August 08, 2009

This is not a mud volcano

Thursday morning, I got home to the sound of the sinks glugging and an unpleasant smell. A quick glimpse at the back drain revealed the problem- sewer clogged up. One rapid response plumber later, we had determined that our line as far as the drop to the main line was clear. As he said to me, “You can hire a mechanical digger, but you’ll save a whole lot of money if you just dig.” So, shovel and pickaxe in hand, down I went.

Three hours later, I had uncovered the downpipe cap, and quickly changed and sponged off (shower would have dire side-effects) to run out to a job interview. I returned to find the following:


Figure 1. Sewerage eruption vent. Note the splash marks on the back fence, indicating minimum plume height.

The plumber used the term “geyser” to describe it, and said that he had to wait for about an hour for it to subside enough for him to get to work. After ponding in the veggie patch, the flow ran under the fence and down the laneway to near the bus stop. And the stench. Oh, the stench.


Figure 2. The laneway to the bus stop was inundated.

This was the point where he called the utility, as only a main line blockage could account for the volume and type of effluent. There were vegetable bits from species we haven’t eaten for yonks, and the shear volume was more than our 100mm pipe could contain. This was a broad-based community based effort, with the curried squirts, greasy logs, and uptight stones of all our neighbors joining into a gray sludge of maximum entropic state.

I’ve been mopping up and sterilizing ever since, despite such complications as the fact that the effluent flow eroded so much dirt away that I had trouble finding fill for the hole. Despite the churning in my tummy and the phantom scent of sludge being imagined by my brain, the worst is hopefully over. I must ask, though:

Do any of you read this blog while eating your lunch?

Thursday, August 06, 2009

The Pacific Ocean is 2.5 trillion km wide

According to Cosmic Variance, the Bones episode on which Sean consulted was transmitted at 8 pm on 9 April 2009. On 12 July 2009 this broadcast was received here in Australia, where I watched the show.

Because TV transmissions are electromagnetic radiation, and travel at the speed of light, we can use this delay to determine the distance between California and Australia. The delay was 94 days, which is 0.26 years. So the distance is 0.257 light years. This is about 2.4 trillion kilometers, or 16,000 astronomical units. Thus the width of the Pacific Ocean (which separates California and Australia) is slightly larger than the distance between Proxima and Alpha Centauri, in the closest stellar system to our own.

Now, some of you may find this hard to believe. After all, surely if you can’t clearly get channel 6, then a TV transmission from 2 and a half trillion km would be hopeless, right?

Not necessarily.

Here in Canberra, our NASA Deep Space Network is currently tracking Voyager 1 at a distance of 110 au. This is 147 times closer than California. Assuming that radio transmission strength follows an inverse squared distance law, the signal from a California radio station broadcasting from the edge of interstellar space would be 22 thousand times weaker than that from Voyager 1 for a given transmitter power.

Luckily, that power is not constant. Voyager 1 has a 20 watt X-band transmitter. In contrast, San Francisco’s KCNS (UHF channel 38) pumps out an effective radiated power of 5000 kilowatts; 250,000 times more power. As a result, even at the astronomical distance at which California lies, the TV stations there still have up to ten times more signal than the old space probe.

Thus, my interpretation of California being on the outer edge of the Oort Cloud is entirely plausible.

The take home message, of course, is that when people accuse Californians of being way out there, they are vastly understating the situation…