Thursday, September 12, 2013


The black mineral in this rock is mica. It looks a little like silver but it is a sheet silicate (phyllosilicate) mineral. Mica glitters in the sun and is very attractive and often confused with more valuable minerals. The formula is

in which X is KNa, or Ca or less commonly BaRb, or Cs;
Y is AlMg, or Fe or less commonly MnCrTiLi, etc.;
Z is chiefly Si or Al, but also may include Fe3+ or Ti.

Usually, there is an abundance of this type of mineral near where gold or other mineralizations are found.

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