Friday, 27 August 2010

Rock Painting at IMA

At the IMA2010 Conference this year they had a variety of things scheduled in addition to Science. There were sporting events, music performances, and rock painting!

I chose to do a free-hand interlace knot:

Thursday, 26 August 2010

The IMA Medalist is a snappy dresser

My interest in clothing and fashion is normally restricted to 12th Century and earlier. I just don’t find the trends that fashion have gone through since then to be pretty. However, I couldn’t help but notice the beautiful black linen which formed the suit worn by Frank Hawthorne, winner of the IMA Medal for Outstanding Contributions in Mineralogy Research. Most modern men’s suits are polyester if they are cheap (and how they can tolerate to wear such a non-breathable fibre is beyond me), or wool if they are nice (much better!), but his is the first I’ve seen in linen (one of my favorite fibers), and despite being in a cut which doesn’t interest me, I couldn’t help but admire the colour (black shirt, black jacket, black trousers, all of a lovely, dark, shiny, new looking shade), and even thought the colour of the dark purple tie looked nice in contrast with the rest of the outfit. (However, I still don’t like the shape and location of ties. What is wrong with nice, contrasting colour collar and hems, like were used in part of the Middle Ages?)
But enough about clothing. What about his talk? That was fascinating. He managed to put an awful lot of very complex information into a fairly short amount of time, and while most of it was totally new information to me, he did it in such a way as I felt like I understood what he was saying the whole time.
His topic was from theoretical mineralogy, focusing on the bond-topological basis of structure stability and mineral reactions. He explained how the bonds between atoms in a mineral can be used to predict the stability of a compound. For simple atoms it is necessary that that the atoms on either side of a bond have roughly matching levels of acidity or baseness, making predictions easy—if the cation and anion involved have just about as much level of acid as base, then the molecule will be stable. He also demonstrated how this principal can be extrapolated up to very complex mineral structures, but while it made sense looking at it as he spoke, I’ll not try to explain it now without the diagrams in front of me.

Wednesday, 25 August 2010

IMA continuted

First of all, I offer thanks to Tuff Cookie over at Magma Cum Laude for resurrecting her In the Humorous Vein series. It had been too long since one of her inspirational posters.
The busy schedule that is a week spent at a conference continues. I succeeded in getting my poster printed on time to put it on the poster board today (Thanks to Robert, the person in charge of helping IMA conference attendees with, well, everything, near as I can tell.)
One of the highlights of Tuesday’s lectures for me was the Element’s lecture by Nigel Kelly on Zircon. Anyone who saw the Zircon issue of the Elements magazine will recall what a useful (and pretty) mineral zircon is. Even though (or because of?) the fact that much of the information in the talk was review for me, having read that issue cover-to-cover I very much enjoyed the talk.
Here is the list of talks to which I’ve actually made it on Monday and Tuesday. There were others which sounded interesting, but, alas, the interesting talks in different areas of specialization often conflict with one another. It was also necessary to miss a few I’d have liked to attend while dealing with the logistics of actually getting my poster printed.

From the session MH111 History of mineralogy: The role of the Carpathian region in the 18th century:
Mottana, A.
The tradition of Theophrastus’ “On Stones” during the early stages of modern mineral science
Rózsa, P.
Sir James Hall’s visit in Schemnitz
Viczián, I.
Letters of German naturalists to Domokos: Teleki, the first president of the Jena Mineralogical Society

From the session H112 The scientific value of mineral beauty:

Garcia-Ruiz, J.M., Canals, A., Villasuso, R., Van Driessche, A.E.S. & Otálora, F.
On the formation of giant crystals of gypsum: the science behind beauty

Gilg, H.A., Krüger, Y., Taubald, H., Morteani, G. & Frenz, M.
Genesis of amethyst geodes at Ametista do Sul, Rio Grande do Sul, Brazil

Giuliani, G.
Emerald gastropod fossils from the Mantecanã mine (Gachalà district, Colombia): a record of the recipe for Colombian emerald formation

Feneyrol, J., Giuliani, G., Ohnenstetter, D., Galoisy, L. & Pardieu, V.
Is the V/Cr ratio a fingerprint of the geographical origin of 'tsavorite' in the Mozambique Belt?

From the session: MH110G – Mineral museums and Historical mineralogy

Müller, A., Rumsey, M. & Ihlen, P.
Historical minerals from the Evje-Iveland pegmatites at the Natural History Museum in London

Langhof, J.
Early 19th century scientific networking – a study in Jacob Berzelius’ mineral collection

From the session: GM72 – Accessory minerals: Tracers of magmatic and metamorphic evolution

Harlov, D.E., Williams, M., Jercinovic, M., Budzyn, B. & Hetherington, C.
Partial alteration of monazite and xenotime during mineral-fluid interaction: implications for geochronology

Finger, F., Dunkley, D. & Knop, E.
Multiple phases of monazite growth in the South Bohemian HP-HT granulites: a chance to constrain the entire timing of metamorphic evolution from subduction to exhumation by Th-U-Pb geochronometry?

Krenn, E. & Finger, F.
Unusually yttrium rich monazite with 6-14 wt.% Y2O3 in a granulite from the Bohemian Massif: implications for monazite-xenotime miscibility gap thermometry

Uher, P., Dianiška, I., Bačík, P., Ondrejka, M., Pršek, J. & Zubaj, R.
Gadolinite and crichtonite group minerals: breakdown products of primary monazite and xenotime in granitic and metamorphic rocks

Today is my poster session—we are meant to be at our posters from 14:00 to 16:00. However, today, at 14:00 is also the second rehersal of the IMA 210 Choir. Therefore I’ve written a note stating that it isn’t too late to join the choir, and inviting one and all to join the author of this poster at the 2nd rehearsal, and promising to return to the poster promptly after rehearsal.

Monday, 23 August 2010

before and after

On Sunday afternoon I did a bit of sightseeing in Budapest, with a local guide—a couchsurfer who had stayed with me when he visited my city of residence back in November. Today I posted some of my photos to Facebook, and included the snippet of information that he’d shared with me—apparently all of the bridges connecting the cities of Buda and Pest were destroyed during WWII, but one of them was re-built in the same style as before the war. This is my photo of that bridge:

And this is a link he shared with me of how it looked in 1946.

Seeing his link had me nearly in tears. War is something of which I can never approve, and photos like that really bring home how truly dangerous they are. But the compare and contrast from the destruction then, to the beauty that is now is a tribute to human nature and our ability to sweep up and start over. May we never lose that ability, may we never cause others to need practice that skill, and may we never need practice that skill for reasons of our own causing.

first day of IMA2010

Today is the first full day of lectures at the International Mineral Association’s 2010 Congress in Budapest. I spent the morning attending lectures on the topic of History. The first talk of the day was _The tradition of Theoprastus’ “On Stones” during the early stages of modern mineral science_ by A. Mottana.

He spoke on the ancient text written by Theoprastus usually called “De Lapidibus”, or “On Stones”, which was written around 313-305 BC. Its arrival to Italy in 1427, brought from Constantinople to Florence by Trancaso Filefo, was one of the important parts of the resurgence/rediscovery of ancient learning in the Renaissance, being the first entire book written on stones and minerals. The source of the document that arrived in Italy in 1427 is thought to have been the Vaticanus graecus 1302, a codex written in Byzantium c. 1300-30.

The lecture opened with a definition of the period of the Renassiance, which started in Italy in 1392 when Manuel Chrysoliora was appointed to teach Greek Language & Literature at the University in Florence, and ended in 1611 when Johannes Keppler published Strena Seu de Nive Sexangula, which was the first mathematical text on crystal structure, and thus an important start to the age of science. From there he touched on the various Renaissance scholars who used this source in their own work, and who did translations, and when. The talk was fascinating, but due to the format (only 20 minutes available) it was necessary for him to hurry over the latter portion of the talk, and my note-taking didn’t keep up. (Any errors in the above are due to my rusty note-taking skills, and not to the speaker).

Saturday, 21 August 2010

My flight to Budapest

I flew to Budapest this morning, to attend the upcoming IMA2010 Conference (Aug. 21-27, Budapest). When I finally turned on the computer this evening there was an e-mail from the conference organizers announcing that this event “includes in its programme 13 plenary lectures: seven IMA2010 Plenary talks and six Elements5 talks (the latter celebrating the 5th anniversary of our excellent journal). The topics cover all representative areas, and they are tailored for a broad audience, while the authors are well-recognized experts in their fields, but also attractive speakers.” They also announce that those of you who weren’t able to come out for the meeting can still follow along at home by listing to their live web casting (end public service announcement).

Because I had a morning flight it was necessary to leave my home at 04:00 to begin my journey to the airport. Therefore I decided to just stay up all night, thinking “I can sleep on the plane”. However, what I failed to consider was that the flight path went along the south side of the Alps, for a rather large portion of the range’s extent. Consequently, while I did nap in the bus on the way to the airport, and at the airport itself, I spent the flight with my eyes focused out the window, enjoying the lovely view. Some of the peaks in the second row in still have snow on them, which sight is balm to eyes that have had to endure summer’s heat. I have no idea where I’ll be going when my current contract ends, but I sure hope it is somewhere that I can see (and walk in!) mountains on a daily basis.

Tuesday, 17 August 2010

Article review: “Metamorphism: from Patterns to Processes”

As a member of the Mineralogical Society of America I receive a paper copy of the journal, Elements, each month. Some of there previous issues have focused upon a specific element or a specific mineral. The June 2010 issue (Vol 6, #3), on the other hand, focuses on Fluids in Metamorphism. Needless to say, as a metamorphic petrologist this caught my attention. I’ve just finished reading the article titled Metamorphism: From Patterns to Processes by Bjørn Jamtveit, who is located at the Center for Physics of Geological Processes at the University of Oslo and decided that it is worth mentioning here.

This article is a very good one for underscoring one of the reasons I am fond of metamorphic rocks: they are pretty! He includes a variety of figures to illustrate the types of changes that happen to rocks as a result of metamorphism (change), with a focus on how those changes are facilitated by the presence of fluids. As a teaser for the article, I have copied his figure 1 below. The first photo is of a dark, fine grained basalt (formed by the cooling of lava after it erupted from a volcano), which contains the minerals augite, plagioclase, and olivine, though the individual grains of each are too small to see at this scale. The second photo is of a lovely eclogite, which contains red garnets, green omphacite, and white clinozoisite, all of which are much coarser-grained than minerals in the basalt. Metamorphic processes are responsible for the transformation of basalts into eclogites.

The differences in the crystal structures of augite-plagioclase-olivine vs. garnet-omphacite-clinozoisite mean that the eclogite is a denser rock (~3.5 g/cm3) than is the basalt (2.9 g/cm3), which, the figure caption tells us, means that the transition from one to the other is important for large-scale geodynamic processes, including basin subsidence and subduction.

In addition to illustrating the beauty of metamorphic rocks, the article also touches upon the factors that cause the change, and how long these processes take. I highly recommend it to anyone curious about metamorphism.

Saturday, 14 August 2010

My host’s great-grand father

When I was in Norway earlier this summer, rather than staying in hotels I chose to couch surf, for much of the trip. There is something quite nice about staying with local hosts; one gets to meet people one wouldn’t have otherwise met, and one gets to learn something about the local area and the people who live there. Or, in some cases, the people who have lived there long ago.
My host in Bergen, when she discovered that I’m a geologist told me about her great-grandfather, who was a geologist, so I looked him up. Tom Barth (1899-1971) published over 200 papers in his life in the fields of mineralogy, petrology, and geochemistry. When he was young he studied with Goldschmidt and Eskola, names that should be well known to anyone who has ever read a basic metamorphic geology text. He was one of the people involved in the early stages of developing an understanding of the way crystal structure works, and was the first to demonstrate that chemically different atoms can occupy crystallographically identical sites.
What fun serendipity that my host while I was traveling happens to be descended from a scientist whose life-work comprised an important part of the framework that was a necessary prelude to my own research.

Thursday, 12 August 2010

What is the difference between contact and regional metamorphism?

In the comments on a recent post I was asked about the difference between contact and regional metamorphism, and thought that the answer deserved to be a post of its very own.
First of all I should remind you that “metamorphism” is about change—specifically the changes that take place in a rock due to changes in temperature and pressure. Each mineral has a range of temperatures and pressures at which it is “stable”. When in that range it exists happily because the pattern of the atoms within its crystal structure is appropriate for the conditions. If there is a large enough change in the temperature and/or pressure the minerals become unstable. If that change takes place slowly enough and the new conditions are held for long enough the unstable minerals will undergo chemical reactions to grow new minerals out of the component elements of the old minerals.
However, if the change is too fast the “unstable” minerals will continue to just sit in their rock, doing nothing. This latter feature is a good thing—without it we would never see high-pressure rocks at the surface. Diamonds are a high-pressure form of carbon, and graphite is a low pressure from of carbon. Their ingredients (only the element C) are the same, but their crystal structure is very different. The carbon atoms in the high-pressure version are packed much closer together than the low pressure version. If the diamonds didn’t come to the surface so quickly they would have been replaced with graphite (or the carbon would have been used to create some other mineral).
So today’s post is about those rocks that experienced new conditions in temperature and/or pressure long enough that chemical reactions happened and new minerals grew in response to the new conditions. There are a couple of ways this can happen: Contact Metamorphism and Regional Metamorphism.
Contact Metamorphism is what happens when something really hot (like a body of magma (molten rock) comes in contact with colder rock. The rocks get cooked, just like when one pours pancake batter onto a hot frying pan. Anyone who has ever made pancakes knows that over the course of the cooking process there is a range of textures to the batter before one flips it to cook the second side. The part against the pan got the hottest. As a result the liquid in that layer is completely cooked away and the solid turns a golden brown (or even darkens to black if left unattended too long), the next layer out from there also becomes firm, but with a different texture than the crust, and the far side of the pancake, which is exposed to the air, is still cool enough in temperature that it hasn’t solidified at all yet.
This is similar to what happens to (relatively) cold rocks that have been intruded by molten rock. The layer of rock closest to the intrusion heats up the most, and any fluids escaping from the rock as a result of the heat participates in the chemical reactions of the “cooking” process, so a suite of minerals grow in the layer closest to the heat source that are indicative of high temperature. The next layer out doesn’t get quite as hot, so a slightly different suite of minerals grows there, and even further away from the intrusion the temperature is lower still, so lower temperature minerals grow.
These sorts of patterns were very helpful in formulating theories of metamorphism in the early days of the development of our science, as geologists could easily find places where the pattern can be traced from completely unaltered “country rock” through a series of gradually more and more metamorphosed rocks right up to the contact with the intrusion. In places where there is good outcrop one can see that the layers form concentrically around the intrusion.
Regional metamorphism, on the other hand tends to involve much larger packages of rocks. It is often associated with mountain building (orogenesis), and happens when an entire region gets buried deep enough so that both pressure and temperature increase. This increase causes new minerals to grow. Regional metamorphism is, often, something that happens over a much larger body of rock than contact metamorphism (which goes a long way to explain why “regional” was chosen as the name). It also, often, takes place at higher pressure than contact metamorphism, since it takes a certain amount of depth to achieve the sorts of temperatures at which the metamorphic reactions take place, and that depth comes with corresponding pressure increase as well as temperature increase. Regional metamorphism takes place at a variety of temperatures and pressures, which have been divided into “facies”. The below diagram is figure 2-2 in Spear’s 1993 book Metamorphic Phase Equilibria and Pressure-Temperature Time Paths. It shows some of the more common “facies” of metamorphic rock. Each facies is defined by a group of minerals that coexist in stable equilibrium in that range for a specific rock type. Therefore we metamorphic petrologists can tell just by looking at which minerals co-exist in a single rock roughly what sort of pressure and temperature the rock was at when the metamorphic minerals grew.

timing is everything

I really should sit down and ready my 1000 words a day of geologic literature earlier in the day. Often what I read is inspiring and makes me want to go and do things for my own research. But, when I read it late at night, like tonight (and, I confess, many other nights as well), I’m too tired to follow through with the inspiration. Sadly, by the time I’ve slept and started a new day I’ve often forgotten the feeling of inspiration and nothing comes of it. Perhaps by stating this publicly I’ll revise my habit accordingly and gain the benefit thereby.

Monday, 9 August 2010

some pretty building stone in an unexpected location

I have just returned from a four day visit to see friends who live in Ireland. I didn’t bring my computer along this trip, so I’ve returned to a fair bit of reading of e-mail/livejournal/blogs/facebook to catch up on. So I’ll just share this pretty building stone from a counter top in the Dublin airport. Lovely stuff, with plenty of garnet, definite foliation, some huge feldspar phenocrysts. No idea from whence it came, but it sure did brighten up the airport part of my adventure to see it.

Monday, 2 August 2010

Why Garnet?

A friend of mine recently asked me “Why garnet?”, and it occurred to me that others might also like to hear one petrologist’s thoughts as to why it is such a well-studied metamorphic mineral.
1. They are pretty!
2. They are very common in a wide rang
e of metamorphic rock types.
3. They are stable across a reasonably broad range of pressures and temperatures of relevance for metamorphism.
4. The often form “porphyroblasts” (metamorphic crystals that are noticeably larger than those which surround them).
5. They are easy to identify in hand-samples—their nice “garnet-red” colour often contrasts with the other minerals in the sample (though some of the less common varieties come in other colours, including green and yellow).
6. They are easy to identify in thin-section (a slice of rock only ~3 microns thick, which means that light transmits through most of the minerals so that one can look at it in an optical microscope): they have a high “relief” (they look like they are taller than the things next to them, even though they aren’t) and they are isotropic (they are solid black when the polarizing filters are crossed, no matter how the stage is turned, making them stand out against the changing bright blues, pinks, and yellows that the other minerals become when the polarizing filters are crossed).
7. They have a rather broad range of possible chemical compositions, with iron, magnesium, manganese, and calcium all able to slot into the same position in the crystal structure (this is part of what gives it a broad range of stable temperatures and pressures) and aluminum and silica can also do a certain amount of swapping one for the other. There are a handful of other, less common elements which can also substitute for others in its crystal structure.
8. They have very slow diffusion, which means that once they reach a certain size the center of the grains no longer get involved in chemical reactions. As a result it is normal for the composition of garnets to be “zoned”, with the center containing more Mn than the rims, and the rims containing more Mg than the core (each of the other major elements also typically change their concentration from core to rim).
We metamorphic petrologists talk about the garnet cores being “armored” by the rims. The rims are, in theory, in equilibrium (or trying to achieve equilibrium) with the matrix minerals at any given time—this means that the minerals present will be participating in the chemical reactions that are causing the growth of some minerals and the dissolution of others. For many minerals the normal grain size is small enough that the reactions involve the entire grains, but garnets often grow large enough that only the outermost shell is involved in the reactions, with the inner portion “freezing” in whatever composition was stable when it was the outer portion.
So, just as an Everlasting Gobstopper (do they still make those candies?) changes colors as you suck on it, so garnets show a range of compositions from core to rim. Part of the changes in garnet composition are due to rare ingredients having been used up making garnet (plus or minus any other zoned minerals present). So Mn, which tends to prefer garnet to any other mineral in metamorphic rocks, starts out “high” in garnet, but there is usually so little of it available in any given metamorphic rock it is soon used up and the garnets have gradually less and less Mn as they grow, until eventually the outer portions have no measurable Mn at all. The other reasons garnets change their composition is due to changes in pressure or temperature. Different recipes of garnet are stable at different pressures and temperatures. So if the conditions change different types of garnet grow on the outside of the pre-existing garnet. These features all combine to make it a very well-studied mineral because of all of the inform
ation one can extract about the history of the rock.

A large garnet in the wild (southwest coast of Tasmania, photo taken by Andrew McNiel):

Garnets (2mm) in thin-section from Collingwood River, Tasmania (also shown are biotite (brown), muscovite (pale but wavy lines), quartz (colorless and without lines + dots in the garnet):

Same garnets as above, but in crossed-polarized light: