Archive for March, 2012

I’m going to India on Saturday mainly just to go to India.   However, in order to justify the trip, I’m giving a talk on Tuesday, 13. March in Bangalore on x-ray tomography.   If anyone happens to be in the area, please come!   I’ll try to post a summary of the key points of the talk up either before I go or right after I get back.

My other goal for this trip to pick up a few pieces of Deccan flood basalt 🙂


Raman Research Institute


High-resolution X-ray Computed Tomography — a non-destructive method to
visualize the interior of solid objects

Elizabeth R. Goeke
Salem State University, USA

Abstract:  Application of High-resolution X-ray computed tomography (CT) to
study the internal spatial relationships in a wide-range of geological
materials has grown in the past decade.   CT scans are non-destructive,
relatively quick to obtain, and a wide-array of measurement and
visualization methods have been developed  to analyze the data.   Comparison
between CT methods and traditional destructive  serial sectioning results in
analyses that closely correspond and are usually within error of each other.
The variation of X-ray attenuation within objects relates closely to density
and is used to differentiate between variations in the materials or phases
within the analyzed sample.  High-resolution CT analysis has a scale of
resolution of approximately ~100 microns, while ultra-high-resolution scans
may reach ~10 microns.   Commercial high-resolution CT scanners are
available and require only counter-top space for setup as well as several
computers to process the data.   In addition to being safe to use on rare
samples such as meteorites and fossils, CT analysis has also been applied to
crystal size distribution studies in metamorphic and igneous rocks,
microstructural analysis of shear zones, characterization of soil and
pore-space morphology, and distribution of economic mineral genesis and

on Tuesday,  13 March 2012, at 11:30 a.m.
Venue: Library Block lecture hall
All  are  welcome

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Hard to believe, but this is my 100th post.   I thought about doing something serious, but honestly, let’s just go with what has been successful for me: garnets throughout my geology career

Garnets in plane light from the Northeast Kingdom of Vermont (BA research):

ERG-25b from the Cow Mountain region of Vermont; garnet inclusions are clearly at an angle to the dominant biotite-muscovite foliation in the rock

Garnet back-scattered electrons (BSE) image from the Connecticut portion of the Bronson HIll terrane (MS research):

BSE image of 99ERG07c

Girl Scouts participating in a Rocks Rock badge workshop (Western Kentucky University, 2002).   We ran the workshop in conjunction with both the Campus Girl Scout troop & the Geology Club the year I taught at Western.

Juniors (4th-5th graders) examining a garnet schist for the rock ID portion of their badge

Wavelength dispersive X-ray spectroscopy (WDS) images from a sample from Payer Land in northeast Greenland (or the PhD project I didn’t end up working on):

WDS mapping of 438965. Garnets are green in the Fe map, blue in the Mg map, and very light in the CP.

In-situ picture of the rocks I did work on for my PhD from Alp de Confin in Switzerland:

bimodal garnet sample that contains kyanite (hard to see without direct sunlight in these samples) from the Adula Nappe

Outcrop photo from a 2007 Vassar field trip to Gore Mt in New York:

amphibole-pyroxene-garnet-plagioclase wall in the upper quarry at the Gore Mt mine

When I taught at the University of Pittsburgh at Johnstown, I started blogging.   At that time I started posting about photomicrographs, including one post about the “jellybean” mylonite from Payer Land.   Hmm, mylonites & garnets together 🙂

Garnet "fish" from the jellybean mylonite.

I started this blog when I moved from UPJ to Gustavus in the summer of 2010.  Over the course of the year, I posted several times during the year about garnets, but the most memorable to me is my summary of the 2010 GSA session in Colorado entitled “Garnet and Its Use in Unraveling Metamorphic and Tectonic Processes”.   Since I didn’t have any pictures to post the first time around, let me just say that garnet research is alive, well, and going in a multitude of directions according to that session.

And last summer I moved back to the Boston area.   Because I’ve only been teaching physical geology & solar system since moving, garnets haven’t come up much in conversation here recently.   In fact, my only garnet-related post was my submission to AW #43 earlier this week.   I obviously need to work on that!

pen & ink drawing of garnet gneiss from Best (1983)

So that’s a 100 posts.   Let’s hope I pick up the pace a bit, add a few more garnets, and hit 200 in less than 18 months 🙂

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What my students discovered for news:

Ok, time to grade more exams.   Fun.   Only a few days to India!

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This is the week right before spring break, so I’ve fallen behind a bit in posting while I was distracted by writing a few exams.   I’m going to India starting on Saturday, so I hopefully can catch up (if not get a bit ahead!) this week.

News stories:

(The impact story was popular as was the Titan story–both had multiple summaries.)

I should get the my physical geology’s summary up later today.

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The deadline for Accretionary Wedge #43 – “my favorite geological illustration” was extended, which finally kicked me into deciding what to post.   There are a number of diagrams I love that people have already used (Erik’s bubble figure, the Wooster fun with chemographic diagrams, MK’s subduction zone — which I’ve drawn on tables at Italian restaurants & on onsies at baby showers).   And then there were the ones that were finalists (Tharp ocean map is awesome, the USGS Volcanic Hazards poster is basically reproduced by students during intro classes, the different types of silicates), but in the end, I had to go for what I truly know — metamorphic thin sections.   Though photomicrographs are gorgeous, to truly “see” what’s going on with textures, you need to draw them by hand.   The old-fashioned pen & ink drawings draw your eyes to the key features — ah, for the days when every department had an in-department scientific illustrator.

The following illustrations are of the progressive syntectonic metamorphism of a volcanic graywacke from New Zealand. The original illustrations are from Best (1982): Igneous and Metamorphic Petrology (W. H. Freeman, San Francisco).

original volcanic rock

burial of our volcanic rocks, which turns up the heat & pressure a bit:

breakdown of some of the hydrous material, recrystallization of material to start to form definite foliation

rock continues to be buried, which increases the amount of metamorphism:

continued breakdown of hydrous phases; beginning of segregation into "felsic" vs. "mafic" lithologies

as metamorphism continues, we finally get to the “good stuff” i.e. garnet 🙂

down to just muscovite & biotite as hydrous phases, with a higher mode of anhydrous garnet + garnet + oligoclase dominating; segregation is more pronounced

My students don’t really appreciate my insistence that they have to draw fields of view during mineralogy & petrology, but the process really helps them “see” what’s going on so much better.   And though most of them are not in the running to become scientific illustrators in the long run, I do really enjoy grading those labs.

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