Mica (silicates): Margarit

Diagnostic card.

Ca Al ₂ (OH) ₂ Al ₂ Si ₂ O ₁₀
Singonia monoclinic
Hardness 4-4,5
Specific weight 2.99-3.08
Cleavage is very good
Fracture is leafy, brittle
Color white, gray, pink, green
Color in powder white
Glitter pearl

Margarit - pearl, or fragile, mica - aluminosilicate. Glitter is pearly. Colors: white, yellowish or greenish. The line is white. Cleavage is very perfect. It's fragile. It is rare. Forms scaly aggregates.

It crystallizes in the form of scaly aggregates, as well as small plates, very brittle, grayish-white or pale-green in color, with cleavage along the base, with pearlescent shine.

Structurally, it is analogous to muscovite, but instead of potassium cations between the packs, Ca2 + cations are located that compensate for the increased negative charge of tetrahedral layers due to the replacement of 50% silicon atoms with aluminum. Margarit almost always occurs in the form of scales or scaly aggregates, individual individuals show a twinning in (110), like mica proper. Usually found in association with chlorites, granules, spinel and other metamorphic minerals.

Diagnostic signs.
In the flame of a candle margarite melts only along the edges. Is susceptible to sulfuric acid.

Origin.
Margarite is characterized by the presence of corundum in deposits. It is often found together with tourmaline and staurolite in chlorite and micaceous shales. Distributed in Tyrol (Austria), in the Urals and in other regions.

Place of Birth.
Margarit occurs in the chlorite schists of the Zillertal in Tyrol, in micaceous emerald-oil shales on the Takova River in the Urals and in corundum deposits in Asia Minor. Often present on the Greek island of Naxos and some places in the states of Pennsylvania, Massachusetts and North Carolina (USA).

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