Clay Doctor - Clay Minerals Society

Dear Clay Doctor: I was riding my motorcycle through New Hampshire when I noticed
flashes of light coming from the road cuts. On closer inspection, I found that the flashes
were sunlight being reflected from mica flakes! The question then occurred to me: Are
there different kinds of mica?
Biker, Hanover
Dear Biker: I also have found that, next to the petrographic microscope, the best way to
study coarse-grain phyllosilicates is on a bright summer day on a Harley at 80 mph. In
answer to your question, there are three major classes of mica: (1) white mica, which
includes muscovite, commonly found in granites; (2) brittle mica, which includes
margarite, a calcium-rich variety; and, finally, (3) Formica, which includes fornikite,
commonly found in Australia.
Commentary
This is one of several Clay Doctors that were aimed at Bob Reynolds, who rode a
motorcycle around Hanover, New Hampshire. There actually is such an outcrop that is
visited by Dartmouth students. Formica, of course, is not a mica at all, but is used to
cover kitchen counters. “Fornikite” uses the Australian pronunciation: “Do you like ta
fornikite, myte?”
Bob Reynolds with his dirt bike
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