Mica
Muscovite (variety of the Mica group) · Mineral Specimen / Industrial Mineral
Crystal System
Monoclinic; often appearing as tabular books or platy/foliated masses with hexagonal outlines
Mineral Group
Silicates; Phyllosilicates (Sheet silicates)
Chemical Formula
KAl2(AlSi3O10)(OH)2
Formation Process
Igneous formation in pegmatites through slow cooling of magma; also occurs in metamorphic rocks like schists and gneisses.
About This Crystal
A silvery-white to pearly mineral with a highly reflective, metallic-like surface. It appears in thin, flexible sheets or 'books' that easily peel away. The specimen shows a vitreous to pearly luster and is translucent in thin flakes.
Physical Characteristics
Color: Colorless, silvery-white, or light grey; Streak: White; Cleavage: Perfect basal cleavage in one direction; Fracture: Micaceous; Specific Gravity: 2.76–3.00; Fluorescence: Generally weak or inert.
Optical Properties
Refractive Index: 1.552–1.618; Birefringence: 0.036–0.054; Biaxial negative; exhibits no notable phenomena like chatoyancy, but has high surface reflectivity.
Hardness & Durability
Origin Region
Found globally; notable sources include Brazil, Russia (Ural Mountains), USA (New Hampshire), and India. Typically found in granitic pegmatites.
Hardness & Durability
Mohs Hardness: 2–2.5; low durability; sheets are flexible and elastic (bend and return to shape) but easily scratched by most minerals.
Care & Maintenance
Extremely delicate; avoid ultrasonic and steam cleaning. Clean only with a soft, dry brush. Keep away from water and oils which can seep between flaky layers. Store separately from harder stones.
Rarity & Value
Common; value is generally low for small flakes, though large, clear 'books' of several feet can be museum-quality. Primarily valued industrially for electrical insulation.
Special Characteristics
Exceptional basal cleavage into paper-thin flexible sheets; high thermal and electrical insulation properties; silvery metallic-like flash.
Lore & History
Historically known as 'Muscovy-glass' as it was used in Russia for windows before glass was common. Traditionally associated with mental clarity, self-reflection, and opening the Crown Chakra.