Some of you may look at the title of this post and be slightly puzzled. After all, I’m a metamorphic petrologist. Who entitled her blog “Life in Plane Light” and has a sequence of posts about photomicrographs. And who has been giving a short summary of what you can do with a petrographic microscope. I think its fairly obvious that I believe in optical mineralogy.
Ok, so why then this post? Saturday morning (5. March 2011), Mickey Gunter at the University of Idaho sent the following email to the MSA-Talk listserv:
All,
A colleague of mine, Dan Kile, who is very active in teaching and research in optical microscopy in the private sector just asked me a question that I could not answer. He was curious if there are ANY dedicated optical mineralogy courses (quarter or semester) STILL taught at the undergraduate level in the United States.
Anyone know of any?
In response, Mickey has received a number of private posts and there have been 23 public responses on MSA-Talk. (That’s the count as of 8 PM CST Sunday night–we obviously don’t take the weekend off!) Mickey has said he’ll summarize the private responses in the near future, so I may update at that point.
Since MSA still doesn’t have an archive of the messages available (I’ve muttered about this previously…), I’m going to give a few of the more memorable arguments here. Almost all have been positive (not surprising considering mineralogists are the probably the most vocal pro-optical microscopy crowd out there), but I want to at least hit the counter-arguments presented as well as some of the other arguments I’ve heard in the past for cutting down on optical.
The optical mineralogy “discussion” is not a new thing. Mickey, who is the co-author of the new mineralogy textbook published by MSA with Darby Dyar, is no newcomer to this debate. In 2004, Mickey published a paper in the Journal of Geological Education (JGE) entitled “The polzrized-light microscope: Should we teach the use of a 19th-century instrument in the 21st century?” (the article is in an entire volume of mineralogy-related papers). Actually, most of the arguments presented in that paper were brought up again this weekend–we seem to repeat ourselves.
Before I get to the pro’s, we need to have a short discussion of what the standards once were, what they morphed into & why, and where things stand today:
- if you have chosen to become a geologist 30-50 years ago, you most likely would have taken one course in “hand-sample” mineralogy, a second in “optical” mineralogy, and then petrology (probably separated into igneous, metamorphic & sedimentary)–this is the “old school” method
- post-plate tectonics into the 80s, some changes were made geology curriculums as to what every student should probably know and several courses were added, which meant that some courses had to merge and mineralogy turned into a one-semester hand sample & optical together course; larger institutions kept an upper level petrography course, but it usually was only taken by the hard rock crowd–this is the method I was taught under
- as time moved on, a large push to cover more “environmental” material came to be as well as the fact that minors & education majors, who might have previously taken both mineralogy & petrology, were getting squeezed for time; a number of departments merged at this point mineralogy & petrology together into an “Earth Materials” class; its hard in just a semester to cover everything, so optical is usually cut in these courses; some institutions managed by turning back to a three-course cycle, just only requiring certain majors to take all three, but unfortunately, some geology majors started to graduate without learning how to use the petrographic microscope–this is what the pro’s in this discussion are trying to avoid
- where we are right now: some places still teaching the “old” method with separate hand sample & optical, but they are becoming far & few between in the US; most seem to merge hand sample & optical into one semester, leaving petrology its own semester; and some are down to one semester to get all of mineralogy & petrology in (for full disclosure: I’ve taught both the 2nd & 3rd type)
The pros for including optical as part of every geology major’s degree (I’ve corrected spelling, but otherwise direct quotes):
- Andreas Moeller (U. Kansas): “For me the foremost reason why I think optical mineralogy is a great teaching device for science majors is that it gives undergrad students a great “research” experience. They get to make detailed observations, need to be meticulous and exact in a variety of measurements they have to make to come up with an interpretation, and because often the solution is non-unique they have to draw on other observations in (rock type, likely chemical composition, does the assemblage “make sense”) to make a decision what the most likely interpretation is. Every thin section is a little research project. It also teaches them to trust (or mistrust) their own observation/data before using more sophisticated gadgets.”
- John Smoliga (Boehringer Ingelheim Pharmaceuticals, Inc.): “I feel that it teaches great problem solving and observational skills that can be applied to other areas outside of geology. The skills I was taught … have served me very well throughout my career in the mining, chemicals, materials science industries, and now heading up a solid-state characterization group in the pharmaceutical industry.”
- Lucie Tajcmanova (Freie Universitaet, Berlin): “The students also should be aware of how important a description of phase relationships in the thin section is before they start to “play” with phase equilibria modeling.”
- Bryan Bandli (U of Minnesota, Duluth): “My first job interview out of grad school was at a consulting lab that specialized in microscopy and microanalysis. After touring the lab and seeing the PLM lab, two SEMs (one FE), the 200 kV TEM with EELS, the FTIR microscope and several other analytical instruments, I was asked “What is the most powerful piece of equipment in our lab?” I said, “The PLM.” I ended up getting the job, I assume in part, because of that response.”
Just a a point of clarification: almost every geology department has a collection of polarized light microscopes (PLM). They may be ancient (I’ve taught with ones that require an external light source!), they rarely seem to match, and they require some upkeep, but the price of a student microscope without bells & whistles is <$5000. SEMs start at at least two more zeros. Microscopes don’t come out of petty cash, but they can last and last and last with proper care. And usually, I can tell within a few minutes while still sitting in my office what is actually in the rock with no carbon coating, pumping out the vacuum, or cranking up the electron beam.
The anti-argument:
- L. Bruce Jones (GemScience Research LLC): “While I believe the disciple and critical thinking necessary to effectively learn optical mineralogy is extremely valuable, from a pragmatic perspective I believe there is a rational and expeditious alternative. [...] Why not simply teach students to use Raman microscopes? The use of Raman microscope is fast and the results are referenced to a database and take little interpretation. The technique is incredibly powerful and the cost of Raman scopes, even confocal ones, are coming down nicely.”
Response to Jones by Jill Pasteris (Washington University):
As someone who has been doing Raman microprobe spectroscopy for almost 30 years, I certainly am impressed with the instrument’s capabilities. Indeed, the relatively modest cost of the new systems make them available to more students. However, this availabitliy has also led to a kind of “point and shoot” mentality that has real drawbacks. For instance, one could move one step further and suggest that geologists could be removed as middlemen here, simply setting trained technical people to the task of making these simple-seeming mineral identifications. If we consider what really makes for an accurate and insightful mineralogist or petrologist, however, it is a background that involves intimate interaction with minerals and an understanding of how all the properties of a mineral are interlinked. Teach the students optical mineral and THEN hand them a Raman microprobe. They’ll be able to understand the rocks, the concrete, the AMD precipitates, etc. much better than someone who was placed very early on a sophisticated tool that has its own often-overlooked complexities.
I believe this discussion occurs again & again because of a number of reason, but the largest may simply be the fact we continue to have it in places that non-hard rock geologists are unlikely to read. This may have to become something referred to not just in MSA & NAGT publications, but on the front covers of GSA Today and AGU’s EOS before we can start the real discussion with all the geologist who don’t use optical in their daily lives & wonder why we should continue teaching it.
A few references:
Optical is taught to a number of professionals by two private firms:
(I have no idea why these two groups have 1) the same last name and 2) are in the same city, but its just shy of $2000 for 5 days of instruction.)
Online & print resources:
- 1996: one of the first SERC workshops to be offered was Teaching Mineralogy at Smith College; in 1997 MSA released a monograph that included exercises, methods, and activities developed by the group (I have a copy on my shelf); the workshop site has been updated over the years, so its a wonderful resource for anyone looking for new ideas
- 2004: the JGE volume on teaching mineralogy that I referred to above
- 2007: an issue of Elements (a joint publication by a number of different mineralogy & geochemistry societies) on Teaching Mineralogy, Petrology, and Geochemistry (related SERC workshops: 2005 Geochemistry; 2003 Petrology)
- 2011: a mixed SERC workshop for Mineralogy, Petrology and Geochemistry will be held this summer in Minneapolis–I’m excited, because I’ll get to attend this one!
Update (Monday, 9.30 CST):
- David Mogk (Montana State) has added a specific page to the SERC website for optical mineralogy resources
- Greg Dumond (U. Arkansas) added: “Most of us also appreciate the dramatic spectrum of scales at which we operate (sub-micrometer to 1000s of km). As a student, I was (and still am) so impressed by the plate tectonic-scale relevance of my “dislocation-scale” observations. My main question is whether we have codified this “utility and necessity” in a formal position statement. Such a statement might prove useful for me as I begin the battle with administrators to remove “Rocks and Minerals” from our curriculum and replace it with Mineralogy and Petrology as two separate classes. Our goal will be to teach petrography and elements of optical mineralogy in both classes. As it stands now, I cannot fathom how we can teach what we normally taught in 4 classes (Mineralogy, Crystallography, Optical Mineralogy, and Petrology) in 1 class (“Rocks and Minerals”)!”
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Papers:
Gunter, M.E., 2004, The polarized-light microscope: Should we teach the use of a 19th-century instrument in the 21st century?: Journal of Geological Education, v. 52, p. 34-44. [open-access]
Elli Goeke
It seems weird to me that the worth of optical mineralogy is even in question. At Portland State University we start the first two geology courses with hand samples and then move onto mineralogy and petrology where use of a petrographic microscope is core to our labs. It’s almost two semesters worth of microscope time.
Last summer I did a project analyzing the calcium content of pyroxene in a meteorite. Had the meteorite professor not been with me, I wouldn’t have known what to look for. Thanks to my microscope time this term, I at least have an idea how to differentiate between olivine and pyroxene (fractures be damned!)
While the electron microprobe and SEM can give you exact mineral make up of a specimen, you need the microscope to allow you to preemptively choose which minerals to scan (in the case of the EMP). At PSU we pay a pretty penny to use the EMP and we have to be super efficient to get all our work done. Our 40 year old petro scopes allow us to do that, so training is vital so as to not waste our very limited resources.
That’s just my two cents on the matter.
I think Winton Cornell had a very good point that he put in a message under a separate string about the use of PLM by graduates of his department who have jobs in the oil and energy industries. He wrote:
“Very little, if any, PLM is done. The larger research labs still do microscopy, but I do not know of any Independents that still do microscopy. Even simple, reflected light microscopy is dying out. And, with the log-while-you-drill technology that’s available, even mud loggers are going away, and as such there is even little well-site geology done these days.”
I interpret this as meaning that the oil industry has found a faster way to collect data that adequately (and definitely more consistently) describes the formations/characteristics they are interested in. It is unfortunate that this efficiency has meant the decreased utilization of PLM. However, PLM analysis has a significant variable that cannot be accounted or corrected for and that is the operator. In a research setting, this is OK but when time is of the essence and making direct comparisons between data from separate labs, it is critical to have data collected in a consistent, reproducible manner.
He later goes on to describe how dual beam SEM-FIB instrumentation is being more commonly used to determine porosity of shales in three dimensions. Doing this sort of analysis is likely not possible with PLM. So that is a bit of an apples to oranges comparison, but when the demand is for data on a smaller scale than can be achieved with PLM, there is no other path but to higher technology.
I think the discussion also is guided by the old cliche that if your only tool is a hammer, every problem is a nail. If students aren’t shown how using a PLM has direct applications outside of “Optical Mineralogy 101″, if they are never given the opportunity to use one to study a geologic problem outside of the classroom, then when they go on to a career position they don’t look to it to help them solve problems they may come across. If they don’t see their professors using the PLM outside of the classroom that has a major impact on their perceived utility of the microscope.
In the mining industry MLA (and QEMscan both trade names) automated mineral analysis by SEM/EDS is taking the place of ore microscopy. The systems are supercharged point counters and can provide phase relations and modal analysis in a matter of minutes and do it in a quantitative manner. Compared to the time required for a human to do the same analysis with an ore microscope it is a no-brainer to choose to use one of these systems.
As a microscopist and mineralogist I hate to see the decreased utilization of human interpretation of direct observations of rocks/minerals with microscopes. But I can understand the drive to have quantitative, reproducible data in as short a time frame as possible.
As someone who works with microstructures and metamorphic reaction textures, I’m horrified that this is eve n a question. (Although if someone wanted to give me a fully equipped SEM, I wouldn’t mind a bit.)
And as someone in a department that does still teach a stand-alone optical mineralogy course… well, the mining industry might not use it routinely any more, but our graduates get jobs (especially in the mining industry) with BS degrees. Part of the reason is that our students are comfortable with rocks, and part of that comfort comes from looking down a microscope, going back to a hand sample, going back to the microscope, etc. Even if we had an SEM, the students wouldn’t all be able to look at their samples at once – they would get a small amount of time with an expensive instrument (except for the ones using the SEM for their senior theses). I think it’s the familiarity that comes with the opportunity to look at samples for oneself, with exploration, that makes our students so comfortable with rocks – and so much in demand by industry.
We know that the optical properties of minerals tie directly to composition and structure. The scientific problem is one of calculating an index of refraction from the composition and structure. For example, the optical measurements are exquisitely sensitive to light-element substitutions, and it is difficult to analyze light elements otherwise. For a simple solid solution, we get a linear relation between index of refraction and composition or unit-cell volume, so an optic measurement gives the composition. People have given up on this method of optical analysis because a theory to deal with complex materials is poorly developed. Also, who wants to deal with toxic high-density immersion liquids in a time-consuming process of index-matching by the Becke-line method? Furthermore, few master the problem of grain orientation for birefringent crystals. Instead, I view the photon as a probe of the bonded structure. The photon refracts at a specific level of energy through a mineral. My approach has been to build an instrument to automatically measure the optics of loose grains using standard rules of reflection and refraction. Then, I calculate the optics from the composition and structure. Using the refraction data, the calculated structure must agree with the composition and structure indicated by analysis of the single-crystal X-ray diffraction data.
God I hope optical mineralogy is still as relavent in the job force, seeing as it is the one aspect of geology and lab work that I absolutely adore. I wouldnt mind at all being a metamorphic or igneous petrographer.