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

Mazdab, Frank K - (fmazdab) fmazdab at email.arizona.edu
Fri Oct 20 16:10:36 EDT 2017


(oops… possible double-reply because mail program picked wrong account… sorry)

Hi Lydia and all,

As a color-blind petrographer as well, I’d like to offer these additional suggestions.

For me at least, plane-light color and pleochroism is definitely much more challenging than ascertaining birefringence.  For birefringence, I go to the grain edges and count the times I see blue (or purple, or however your student may interpret that dark color).  First order colors are usually straight-forward since grays and yellows and oranges are probably recognizable, and then once the blue (or purple) fringe appears you go up an order.  I generally don’t have students try to differentiate blue from blue-green, green from yellow, or purple from blue (since I have trouble with these), and so I suggest the student use terms like “low 2nd order” (in lieu of 2nd order blue-green), “mid 2nd order” (in lieu of 2nd order green or yellow), or “upper 2nd-low 3rd order” (in lieu of guessing the particular shade of red/purple/blue near the boundary).  It adds a bit of extra error into the birefringence assessment, but since minerals generally show a lot of birefringence variability anyway due to compositional variation, slightly thick or thin sections or simply not being quite oriented to show max birefringence, I don’t worry too much about an exact color.  For conversion to numerical birefringence, I always tell students to be flexible and add their own personal “error bars” to their assessment.

In contrast to birefringence, plane-light color and pleochroism can be a bear, however.  The one I always especially hated and is mentioned in every petrography text is the pink to green “supposed” pleochroism of hypersthene… fake news… LOL.  In a non-exam situation, I always suggest to students with color vision issues to ask their neighbors, and so they don’t feel self-conscious about it, I make sure at the start of the semester to note that I’m color-blind and when I circulate among students in lab I actively ask things like “I’m guessing this is green… am I close?” or “this is either yellow or green” when I’m asked about a color, so they know it’s OK to ask and not be embarrassed.  As Lincoln noted earlier, we color-blind guys do sometimes have an advantage.  I can readily recognize the very pale green (or is it yellow?) of an almost Fe-free diopside in marble, whereas those with normal color vision generally don’t notice any color difference from the surrounding carbonate.  In an exam situation, I try not to ask color-specific questions, and as others have mentioned, emphasize examples that offer other properties that would be useful (e.g. hypersthene samples where the cleavage, relief and associations stand out, although admittedly nature may not always be so helpful).

I disagree with Dave about the utility of mineral atlas (full disclosure... I’m the author of one), and so I neither encourage nor discourage their use.  A student may not be able to “name” a color, but a comparison with a photo (ideally many photos) may allow a student to say the colors look similar.  And it may also remind a student to notice other features (e.g. relief, associations, morphology, etc.) that a student may accidentally disregard after being initially overwhelmed with a color.  I do agree with Dave, however, that it has to be emphasized that minerals are diverse, and if students expect their sample to look exactly like one pictured in a book, they may be looking for a very very long time.  For fun (never for an exam), I’ve shown graduate students who rely too heavily on these atlases a thin section with bright blue staurolite (Co-bearing) and ask them to find that photo in their book… that usually brings home the point about both the reliability of color as a diagnostic tool and that mineral atlases don’t always have the easy answer.

I’ll conclude this because it’s starting to get long.  I will say that one area in optical mineralogy that I haven’t found many ways to get around my color vision issues is in reflected light petrography.  With many minerals described with such awful (for color-blind people) terms as “pink-gray” or “brownish-cream” or “bluish-gray, but not as bluish as…” or “bright white but less reflective than… (which it has to be adjacent to)”, I’ve conceded defeat in this field.  Thank goodness for the microprobe, where all my opaque minerals eventually end up.

Frank
On 19 Oct 2017, at 14:39:41, 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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Frank K. Mazdab
analytical mineralogist
Department of Geosciences
1040 E. 4th St., Gould-Simpson Bldg. (Bldg. 77)
University of Arizona
Tucson, AZ 85721

fmazdab at email.arizona.edu<mailto:fmazdab at email.arizona.edu>
office: rm 342 Gould-Simpson Bldg.

www.rockptx.com<http://www.rockptx.com>

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