Muscovite (Mica)
Faceted Mica is virtually nonexistent because of the perfection of the cleavage and the variable hardness within crystals, not to mention that it is rarely found as translucent crystals. Fuchsite, Lepidolite, and Muscovite are three members of the Mica family. Muscovite has a Mohs hardness of 2–2.25 and when comes to its crystal habit is crystals tabular to columnar, striated, pseudohexagonal or diamond-shaped, to 4.5 m and 77 t. The density of this stone is 2.77- 2.88 (g/cm3). As stellate aggregates, plumose, globular; scaly, granular, compact massive. Fuchsite is colored deep green with chromium impurities and is commonly available as cabochons. Lepidolite is a sleepy, pale pink color and is an extremely rare gem.
| Category: | Phyllosilicate |
| Formula: | KAl2(AlSi3O10)(F, OH)2 |
| Hydrated phyllosilicate mineral of aluminium and potassium | |
| Crystallography: | Monoclinic-Prismatic |
| Crystal Habit: | Crystals tabular to columnar, striated, pseudohexagonal or diamond-shaped, to 4.5 m and 77 t. As stellate aggregates, plumose, globular; scaly, granular, compact massive. |
| Twinning: | Composition plane [001], twin axis [310], forming six-pointed stars. |
| Cleavage: | [001] Perfect, Parting on [110] and [010] |
| Fracture: | Micaceous |
| Tenacity: | Tough; laminae flexible and elastic |
| Hardness (Mohs): | 2.0 – 2.5 |
| Density: | 2.77- 2.88 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Barely Detectable; GRapi = 140.52 (Gamma Ray American Petroleum Institute Units) |
| Color: | White, Gray, Silver White, Brownish White, Greenish White |
| Transparency: | Transparent to Translucent |
| Luster: | Vitreous to Pearly or Silky |
| Refractive Index: | 1.552 – 1.618 Biaxial ( ? ) |
| Birefringence: | 0.0340 – 0.0420 |
| Dispersion: | Weak to Distinct; r > v |
| Pleochroism: | Weak when colored |
