igneous

Muscovite Mica (Granitic Pegmatite)

Muscovite - KAl2(AlSi3O10)(OH)2

Hardness: 2.5–3 on Mohs scale; Color: Silvery-white, gray, or faint green; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect basal (peels into thin sheets); Specific gravity: 2.8

Hardness: 2
Color: Silvery-white, gray, or faint green
Luster: Vitreous to pearly

Identified March 4, 2026More igneous →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed in granitic pegmatites during the final stages of magma crystallization where mineral-rich fluids cool slowly, allowing for large crystal growth. Common in mountain belts of various ages from Precambrian to Mesozoic.

Uses & applications

Used as an electrical insulator in capacitors, a filler in paints and plastics, and as pearlescent flakes in cosmetics. Historically used for oven windows (isinglass) and cold-weather windows.

Geological facts

Muscovite is the most common mica and can form 'books' that are several feet across. Its name comes from 'Muscovy-glass,' a term used in Elizabethan England because it was used as cheap glass in Russia.

Field identification & locations

Identify by its 'peelable' sheets and silvery reflection. Commonly found in coarse-grained igneous rocks like granite. Collectors should look for intact 'books' or hexagonal crystals without edge fraying.

Other igneous specimens

See all

Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral