Crystal Muscovite

Chemical Formula

KAl₃Si₃O₁₀(OH)₂

Composition

Basic potassium aluminum silicate, sometimes with some chromium or manganese replacing the aluminum

Variable Formula

K(Al,Cr,Mn)₃Si₃O₁₀(OH)₂

Color

Colorless, white, beige, yellow, brown, gray, green, pink, purple, red, black; occasionally multicolored

Streak

Colorless

Hardness

2 - 2.5

Crystal System

Monoclinic

Crystal Forms 
and Aggregates

Crystals are in thick flakes, micaceous masses and groupings, and in tabular, foliated, flaky, and scaly forms. Crystals may also be elongated with one dimension flat, or stubby triangular or hexagonally shaped crystals. Muscovite also forms interesting aggregates of dense bladed crystals, thick rosettes, uniquely twinned star-shaped formations, and rounded botryoidal and globularmasses of dense flakes.

Muscovite may also form pseudomorphs after other minerals, assuming the original minerals crystal shape.

Transparency

Transparent to translucent

Specific Gravity

2.7 - 3.0

Luster

Pearly

Cleavage

1,1

Fracture

Uneven

Tenacity

Sectile, Elastic

Other ID Marks

Tendency for small pieces or flakes or peel off.

In Group

Silicates; Phyllosilicates; Mica Group

Striking Features

Flaky habit, crystals, sectility, and mode of occurence.

Environment

Muscovite is a very common rock-forming mineral and is an important constituent in many environments. Its presence is noted especially in granite pegmatites, in contact metamorphic rocks, in metamorphic schists, and in hydrothermal veins. Important Muscovite deposits where large significant crystals occur are almost exclusively from granite pegmatites.

Rock Type

Igneous, Metamorphic

Popularity (1-4)

1

Prevalence (1-3)

1

Demand (1-3)

1