Posts Tagged ‘optical mineralogy’

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:


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:

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”)!”



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]

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