Margarite

This article refers about a member of the mica group, and should not be confused with "margarita".

Margarite
240px 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
Identification
Color	flesh pink
Crystal habit	platy
Crystal system	monoclinic
Cleavage	basal
Mohs scale hardness	4

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.

References

• Deer, W.A., R.A. Howie, and J. Zussman (1963) Rock-forming minerals, v. 3, Sheet Silicates, p. 95-98.
• Mindat with location data
• Webmineral data
• Mineral Data Publishing PDF