Margarite - Encyclopedia

    Class : Silicates
    Subclass : Phyllosilicates
    Crystal system : Monoclinic
    Chemistry : CaAl₂(Al₂Si₂)O₁₀(OH)₂
    Rarity : Uncommon

Margarite is a fairly rare mineral from the micas group. It is, with clintonite, one of the "hard" micas, in which calcium is the main interfoliar cation, a property which results in cleavage blades that are harder and less elastic than in classic micas, such as muscovite or biotite. A partial replacement of Ca by Na commonly occurs, ensuring an incomplete transition to paragonite. Margarite is a metamorphic mica which is found in aluminous rocks of low to medium degrees of metamorphism (chloritoschists, mica-schists, etc...), usually associated with corundum from which it seems to derive by alteration, and with diaspore. Its name comes from the Greek margarites (pearl), in reference to its pearly luster. Margarite indeed has a vivid pearly luster on the perfect {001} cleavage. It is pearl white to grayish, pale pink, yellowish or greenish in color, and most often appears in disordered aggregates of small strips, rarely in pseudohexagonal tabular crystals reaching 3 cm for the largest. The twins are identical to those of other micas.

Main photo : Margarite from Chester Emery Mines, Massachusetts, USA © Henry Minot

Twins are known on the composition plane {001}, with the axis [310].

No fakes recorded for this mineral species.