is a calcium rich member of the mica
group of the phyllosilicates
with formula: CaAl2
. 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.