Wednesday, November 24, 2010

Extrapolation of the likely composition of a mineral from mixed analyses

I have mentioned before the difficulties of using a microprobe to analyze very small phases. The electron beam with which we do the analysis can, with care, be focused to about 1 micron diameter (remember that there are 1,000 microns in every millimeter). However, should the mineral phase of interest be smaller than one micron, in any dimension, the analysis will yield the composition of not just that mineral, but of whatever happens to be next to it as well.

The below photo shows one of my experiments for which this was a problem. As with all back-scatter electron images the amount of brightness or darkness of any given part of the image is based on the composition of the sample in that location. Brighter areas contain more heavy elements, darker areas more light elements. The brightest grains in this image are the large pale grey crystals, which often have dark centers; these are garnets. The dark centers are the pyrope (Mg-garnet) seeds that were included in the experimental powder to give the new garnet, which is much higher in Fe (iron), a place to start growing from. The narrow stick-shaped crystals which occur in a group on the left hand side of the image are chloritoid. Unfortunately, as you can see by the scale bar on the bottom of the image, they are too narrow to obtain a good analysis. Through careful searching of the sample we found a few places where the chloritoid grains were slightly larger than the others—these were the ones we analyzed, in hopes that we would be lucky. Alas, 15 times we tried, and 15 times we failed to obtain an analysis which was only chloritoid, but instead they were "mixed" results of both chloritoid plus another phase.


How do I know for certain that they are mixed? Look at the below graphs and you can see for yourself. The upper graph shows the composition of all of those mixed analyses with respect to how much aluminum and how much silica they contain (blue-green hollow triangles). It also shows the region (grey circle) within which all of the matrix mica in this sample plots, and the location of where kyanite (Al2SiO5), also present in this sample, plots. As you can see, there is a clear trend going from the solid green triangle towards the mica, and another trend going from the solid green triangle towards the location of kyanite. The lower graph shows the trends for iron vs aluminum. By plotting this data for a variety of different combinations of elements I have come up with my best guess as to the composition of chloritoid is in this sample (solid bluish-green triangles). Is it as accurate as if I'd been able to get a good measurement? No. Does it give me information I can use when doing other parts of my data analysis? Yes, yes it does. Playing with graphs is one of the fun parts of my job—the information they convey communicates so very clearly.


Friday, November 19, 2010

Final experiment of the project

What is probably my final experiment (for this project) is running. We started it yesterday morning. My current contract runs through December. At 2 to 3 weeks per experiment, this one is probably it. This fact left me torn as to what conditions to choose for the run.

I've got a couple of previous experiments which turned out to be very difficult to analyze due to improper sealing of the capsules. Therefore I'd love to re-run them, with properly sealed capsules, in hopes of better grain sizes, so that I can get good analyses of the phases present.

We've got some data from experiments run by a predecessor of mine which use a slightly different bulk composition. In theory the difference between the two bulk compositions shouldn't really matter—most of the difference is in the amount of SiO2, which is still in excess in the bulk composition I use (as we can tell from the presence of quartz). However, when I calculated what phases should be present for each bulk composition using Perple_X, it said that at the P/T of those old runs the new bulk should have different phases. Therefore I'd like to re-run one of those to see if there is, in fact, any difference in the results with the slightly different composition.

And, finally, both my boss and I wanted to do another run in a P/T space that is expected to have both garnet and talc, since this project is about defining the stability field for talc. That makes three different experiments I want to run, and sufficient time available to do one of them. Decisions, decisions!

We eventually decided to go with a totally new run—while the data from the "bad" runs isn't complete, we do know that there isn't talc present at those conditions, which is the single most important question. Therefore there is more value in obtaining new data than clarifying old data in this case.

All in all, this project has convinced me that 1.5 years is simply not enough time for such a project. However, I am pretty certain that if it had been a 3 year contract that was now approaching its end I'd still be sitting here thinking about the other experiments I would have liked to have run, had there been time/budget to do so. Ah, the life of a research scientist—so many questions to be asked, so many things to do to try to answer them, but no matter which ones we choose, it never, really, feels like we've got time enough to obtain all of the data we would like to have…

Wednesday, November 17, 2010

What is the deal with Academic Conferences, anyway?

In a comment to yesterday's post I was asked "What's the deal with academic conferences? Do you have to be within the correct academic circles to attend or is there some degree of public allowance?" I started to type up a reply, and then realized I had enough to say on the topic to warrant making a separate post on the topic.

Most academic conferences are open to anyone willing to pay the admission fee, which is often higher for people who aren't a member of the sponsoring organization. However, it is often worth purchasing a membership to the organization if you wish to attend their conference, as the amount you save on registration fees is larger than you'd spend on the membership, particularly if you are a student, since student memberships are usually quite affordable compared to the "professional" membership rate). If all you want to do is attend as a audience member, hear the talks, have coffee with the folk there, check out the info booths and see what is being sold in the booths offering stuff for sale all you need to is pay the registration fee and you are good to go.

However, If you want to share your research with others you need to look over the various sessions being offered, find one wherein your research fits the theme, prepare an abstract describing your research, submit it (and the abstract submission fee) before the deadline *and* register to attend the conference (and pay the registration fees, too). Often when submitting an abstract they ask if you prefer to do your presentation as a poster or a talk. However, even if you choose talk you might wind up doing a poster anyway; if they have too many talks offered for a session they will choose some of them to be posters instead. It is also possible that a session won't accept someone's abstract at all, but I have yet to see an example of this.

Another reason to attend conferences (at least in Geology, but possibly in other sciences, too) are the pre-, post- or mid- conference field trips. Most conferences offer 1 to 5 day trips to look at the highlights of local geology, with the trip led by people who have long worked in the area. These are excellent opportunities for networking, and, more importantly, they tend to showcase some of the best outcrops available in a region, so there are many opportunities to increase your photo collection of interesting geologic features, or to add to your sample collection (note: not all areas permit sampling—please listen to the rules at the start of the trip and respect them).

Short courses are another highlight of many conferences. There are often courses on speciality topics that are held at the conference because it saves the students the travel costs—much cheaper to attend both on one trip than to do to separate trips. Note that field trips and short courses are usually priced separately from the conference registration. Luckily, students who enjoy funding that includes conference attendance can usually attend courses and/or field trips without having to pay for them out of pocket (or, at least get reimbursed afterwards).

The final reason to attend conferences is the social aspect. This varies from one to the next, but I have seen offerings ranging from Ice Breaker Cocktail nights, to Conference Dinners, to Ceilidh Dances, to Choir rehearsals/performances to sporting events.

I may have missed the GSA meeting, but…

I just saw a post by Life in a Plane Light which really makes me wish that I had been able to attend the Fall GSA meeting this year. As a metamorphic petrologist I love garnet. Sure, it is a pretty mineral, but the usefulness of this mineral in learning about the history of metamorphic rocks is what makes it truly fascinating. Fortunately, while I may not have been able to attend the session on Garnet and Its Use in Unraveling Metamorphic and Tectonic Processes , the abstracts are available on line to read at will. I've just done well more than my 1000 words of reading from the geologic literature reading these abstracts, and wondering why I hadn't thought of looking at the program sooner. Just because one can't attend a meeting doesn't mean one can't benefit from the information that is shared there.

Monday, November 15, 2010

The difference between moving where one must and where one can

When I was a child my father was in the Air Force. As a result I lived in 4 countries on three continents before I was 7 years old. When I was little moving was something that happened every 1 to 3 years—we went when dad's orders to move came in, and we went where they told us to go; often with not much advance notice. Then my parents split, and the next couple of times I moved it was at my mother's whim when and to where. After I turned 18 I resumed moving every few years, and became accustomed to being the one in control of where I went, when, and for what reason.

It wasn't until my PhD was drawing to a close two years ago that where/when I moved once again became something over which I have little control. Two years ago, knowing that my funding had run out and that I really like the part where I can afford to eat, I begun to apply for every post-doc and teaching position I could find that sounded even sort of interesting, regardless of where it was located. One of those applications resulted in a job offer in Europe, and, as soon as I finished my thesis, off I went.

Now I am once again in the position of applying for every interesting sounding job I hear about. I have chosen not to apply to a couple because of location, but I have also chosen to apply for a couple for which my CV isn't a perfect match because the location is so appealing. In a way I feel almost like I'm a kid again, waiting for dad to get his orders that tell us where we are going, and when. I love moving, but 1.5 years in a large city, even one with lots of trees lining many of the streets (and, most importantly the street upon which I live and upon which my office is located) has convinced me that it would be nice if I could move someplace I would love. Somewhere with mountains, lots of nature/wilderness easily accessible.

Some of the job applications I send in are much like lottery tickets—they might not pick my numbers as the winner, but if I don't enter I haven't got a chance. Others I apply for because I know that my CV is a very good match for what they are seeking, and I feel obligated to apply, despite the location. Which will it be? When will I find out? Life is, as always, an adventure!

Thursday, November 11, 2010

Does anyone remember this story?

Sometime back in the 1980's I subscribed for a year or so to the Magazine of Fantasy and Science Fiction. During that period of time I read a short-story (probably in this magazine, but possibly elsewhere) which involved a person who was able to see a different landscape than the one which is currently present—able to see different plants and animals than are currently living. I think that the people in the story worked out which geologic period (s?)he was seeing by comparing the descriptions of what was seen with a geologic map. Alas, I read that story before taking my first geology class. Now that I am a geologist, I would love to go back and read it again. However, I have no idea what it was called, who wrote it, or even if the geology part was a minor interesting side part of the story, or the overriding plot device. Do any of you remember reading this story?

Sunday, November 7, 2010

this is delightful!

I just saw a link over at Earth Learning Idea to a delightful web page, made by Cary and Michael Huang, which shows the scale of the universe. They've got a blue box you can slide back and forth, to see things at all scales. A very delightful toy.

Friday, November 5, 2010

Time to work, time to play

The November Scientiae Carnival asks: "What is the best part of your job/life as a scientist, and what is the worst part?"

For me the answer to both has got to be the freedom to set my own schedule. I love the fact that I can work whenever I want/feel inspired/have energy, so if I feel like working all night long (like much of this week), I can do so. However, the down side to such a schedule is that it can be difficult to take time off without feeling guilty for not working. People who have jobs which require them to be there at specific hours are free to play during their non-work hours. Those of us who have jobs which aren't tied to a clock, on the other hand, may be free to select which hours are work and which are play, but it is easy to get caught in the trap of thinking during play that one should be working.

Wednesday, November 3, 2010

Folded tracks

One of the things that holds the most appeal for me in the science of geology is the physical expression of deformation. Folds are pretty! I love to see folding in rocks, at all scales. Today I saw a beautiful photo of folding in response to deformation that isn't in a rock. Go over to Dave's Landslide Blog for some amazing photos of the bending of some rail-way track in New Zealand in response to their large earthquake earlier this year.