Clintonite Group – Margarite Composition and Structure

The mineral of this group are rare species that lie between the true micas and the chlorites. They resemble the micas in crystals forms, cleavage, etc., but differ physically in that their folia are brittle, and chemically in that they are basic in character. The only species in the grow that warrants description is margarite.

Margarite
A micaceous mineral with the composition H₂CaAL₄Si₂O₁₂. Monoclinic but seldom in distinct crystals. Usually in foliated aggregates. Perfect basal cleavage. H. = 3.5-4.5 (harder than the true micas). G. = 3.05. Luster vitreous to pearly. Color pink, white and gray. Traslucent. Folia somewhat brittle. Fuses at 4-4.5. unattached by acids. Occurs usually with corundum and apparently as one of its alteration products. Found in this way with the emery deposits of Asia Minor; on the island oe the Greek archipelago; at Chester, Massachusetts; Chester county, Pennsylvania; with corundum deposits in North Carolina, etc.