[MSA-talk] Tips for helping color-blind students with optical mineralogy

Mogk, David mogk at montana.edu
Fri Oct 20 10:16:11 EDT 2017

Hi Lydia,
I am also color blind (or at least color deficient). Although color is a useful determinant, it can obviously also be misleading as the wonderful world of minerals has such variation in color due to solid solutions, and the colors that are seen in thin section may also be an artifact of poor preparation related to uneven thickness…. So, I tell my students that color can be misleading so beware.

I’ve had to compensate by emphasizing all the other optical and physical properties available to us.  I agree with Linc, index of refraction/relief helps a lot , and I also encourage students to look carefully at all the other properties such as cleavage, form, habit.   When using the accessory plate for either optic sign determination, or for length characteristics, I always check the signal  (addition or subtraction) in the preferred orientation, and then rotate 90 degrees to confirm that the interference colors have “gone up or down”  compared with the original position. A quartz wedge can help rather than the 1 lambda plate if you have one.  Pleochroism largely remains a mystery to me.  I also insist that students do the full range of diagnostic tests prior to making the identification (relief/RI, habit, cleavage, iso/uni/biaxial, positive or negative, 2V, length fast/slow, etc.  I don’t let them get away with “That mineral looks like X…”.  It all has to be based on the evidence. Also, as beautiful as the various Atlases of minerals in thin sections are, I discourage students from using these because the images are a singular representation of minerals that often have great diversity in forms, etc., and they think that all instances of a mineral must look like the picture in the book.  If the students do the full slate of diagnostics, they will get the right answer. And color is just one of many observations that can be made.

The great thing about optical mineralogy is that it really is all about doing a series of systematic tests  that lead to a verifiable answer. And the mineral has to “make sense” in the geologic context, chemical system, assemblage---so these are additional checks on whether a mineral ID  makes sense  or not.
Hope this helps, and do affirm to your student that mineral optics is important and useful. And yes, many of us do optics without relying (much) on color.
Rock on!
Dave Mogk

From: <msa-talk-bounces at minlists.org> on behalf of "Lincoln S. Hollister" <linc at Princeton.EDU>
Date: Friday, October 20, 2017 at 5:53 AM
To: Lydia Fox <lkfox at pacific.edu>
Cc: "msa-talk at minlists.org" <msa-talk at minlists.org>
Subject: Re: [MSA-talk] Tips for helping color-blind students with optical mineralogy

Hi Lydia,

As you may remember, I am very color blind.  However, optical mineralogy does not rise to the level of disability abuse that computer graphics has risen to, but that is another story.

For optical mineralogy I quickly learned that relative index of refraction (relief) was more reliable for identification than color.  Colors can often be misleading and not according to the book.  So it is just a question of the becke line at grain boundary, between known mineral and unknown.

Many color blind people see yellow very well.  Tell your student he (note student must be a “he”) will likely do very well with staurolite, which is pleochroic in shades of yellow.  Regular people can’t see this, in many cases.  So I spent lots of my career on the study of staurolite.


On Oct 19, 2017, at 5:39 PM, Lydia Fox <lkfox at pacific.edu<mailto:lkfox at pacific.edu>> wrote:

I am looking for tips to help a color-blind student who is really struggling with the optical component of my course this semester.  I’d appreciate any ideas you can pass along!

Lydia Fox

Lydia K. Fox
Department of Geological & Enviornmental Sciences
University of the Pacific | 3601 Pacific Ave | Stockton, CA 95211| p. 209.946.2481|

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