Margarite

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This article refers about a member of the mica group, and should not be confused with "margarita".
Margarite
Margarite-181325.jpg
Margarite from the Wright Mine, Chester Emery Mines, Chester, Hampden County, Massachusetts, USA. Size: 4.8 x 3.4 x 2.6 cm.
General
Category Micas (phyllosilicates)
Formula
(repeating unit)
CaAl2(Al2Si2)O10(OH)2
Strunz classification 09.EC.30

Margarite is a calcium rich member of the mica group of the phyllosilicates with formula: CaAl2(Al2Si2)O10(OH)2. It forms white to pinkish or yellowish gray masses or thin laminae. It crystallizes in the monoclinic crystal system. It typically has a specific gravity of around 3 and a Mohs hardness of 4. It is translucent with perfect 010 cleavage and exhibits crystal twinning.

It occurs commonly as an alteration product of corundum, andalusite and other aluminous minerals. It has been reported as forming alteration pseudomorphs of chiastolite along with muscovite and paragonite. The margarite in this occurrence forms preferentially along the dark graphite rich inclusions with the chiastolite crystals.

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