“Old geologists never die; they just cross their nicols and rotate to extinction.”
(Elga Gemst, 1978)

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Pyroxene and Amphibole Diagram Mystery

Years ago I noticed a strange coincidence concerning the shapes of commonly taught diagrams concerning the compositions of pyroxenes and amphiboles, and their structures viewed perpendicular to their c-axes. Periodically I would think about why the pyroxene composition and structure diagrams were nearly identical, and the same for the amphibole diagrams, and I would ask friends about it, especially if I considered them to be astute mineralogists. Thus far, nobody has offered an explanation, and the mystery remains. It seems to be too much correlation to be coincidental, but I haven’t yet devised a plausible explanation.

Header photomicrograph of euhedral hornblende with biotite replacement, from the West Charleston gabbro-diorite, NEKB, VT

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