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Muscovite  (Mica)
Current inventory:  0 gems
 

Chemistry:  KAl₂[(OH)₂|AlSi₃O₁₀]
[Potassium aluminum silicate hydroxide fluoride]

Discovered in 1850;   IMA status: Valid (pre-IMA; Grandfathered).
The name was first used in 1850 by Dana and is derived from the term "Muscovy glass," which was in common use at that time; it is in reference to the Muscovy Province in Russia.

Classification

Mineral Classification:

Silicates

Strunz 8th Ed. ID:

8/H.10-70

Nickel-Strunz 10th Ed. ID:

9.EC.15

9 : SILICATES (Germanates)
E : Phyllosilicates
C : Phyllosilicates with mica sheets, composed of tetrahedral and octahedral nets

Related to:

Mica Group, Muscovite Series.

Crystal Data

Crystallography:

Triclinic - Pinacoidal

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.

Physical Properties

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)

Optical Properties

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

Occurances

Geological Setting:

A common rock-forming mineral, in phyllites, schists, and gneisses; in granites, granite pegmatites, and aplites. Formed from other minerals under hydrothermal conditions; may be detrital or authigenic.

Common Associations:

Biotite, Plagioclase, Potassic Feldspar, Quartz, Topaz, Tourmaline

Common Impurities:

Cr, Li, Fe, V, Mn, Na, Cs, Rb, Ca, Mg, H₂O

Type Locality:

n/a

Year Discovered:

1850

View mineral photos:

Muscovite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

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. Fuchsite is colored deep green by chromium impurities and is commonly available as cabochons. Lepidolite is a sleepy, pale pink color and is an extremely rare gem.
 

  
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