Posted by mining | Posted in mica | Posted on 19-01-2012
The mica group of sheet silicate (phyllosilicate) minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition. The highly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms.
The word “mica” is derived from the Latin word mica, meaning “a crumb” and probably influenced by micare, “to glitter”.
Mica classification
Chemically, micas can be given the general formula
X2Y4–6Z8O20(OH,F)4
in which X is K, Na, or Ca or less commonly Ba, Rb, or Cs;
Y is Al, Mg, or Fe or less commonly Mn, Cr, Ti, Li, etc.;
Z is chiefly Si or Al, but also may include Fe3+ or Ti.
Structurally, micas can be classed as dioctahedral (Y = 4) and trioctahedral (Y = 6). If the X ion is K or Na, the mica is a “common” mica, whereas if the X ion is Ca, the mica is classed as a “brittle” mica. Read the rest of this entry »