Biotite Schist
Biotite Schist · Mineral Specimen / Metamorphic Rock
Crystal System
Monoclinic (for biotite flakes), foliated metamorphic rock habit
Mineral Group
Silicates (Phyllosilicates)
Chemical Formula
K(Mg,Fe)3(AlSi3O10)(OH)2 in a metamorphic matrix
Formation Process
Regional metamorphism of pelitic sedimentary rocks like shale or mudstone under moderate to high temperatures and pressures
About This Crystal
A coarse-grained metamorphic rock dominated by glistening, dark brown to black biotite mica flakes showing a distinct foliated and flaky texture with a reflective, pearly to sub-metallic luster
Physical Characteristics
Dark brown to black color, white to gray streak, perfect basal cleavage in individual mica flakes yielding thin elastic sheets, uneven fracture, specific gravity around 2.7 to 3.1, brittle overall rock with flexible flakes
Optical Properties
Biotite exhibits strong pleochroism under a microscope from pale yellow to dark brown; the aggregate displays strong spangled metallic reflection from individual mica cleavage planes
Hardness & Durability
Origin Region
Worldwide metamorphic terrains including Scandinavia, the Appalachian Mountains in North America, and the Brazilian Highlands
Hardness & Durability
Mohs hardness of 2.5 to 3 for the biotite flakes and around 5 to 7 for the quartz-feldspar matrix; low durability due to perfect cleavage and tendency to flake apart
Care & Maintenance
Store in a dry place, handle with care to prevent flaking, avoid moisture and harsh chemicals, clean gently with a soft brush without water
Rarity & Value
Common, valued primarily as an educational mineral specimen or decorative stone rather than a gemstone; inexpensive price range
Special Characteristics
Glistening spangled appearance caused by the reflection of light off millions of aligned mica cleavage planes (schistosity)
Lore & History
Used in geology education to demonstrate regional metamorphism and foliation; in metaphysical lore, mica-rich rocks are sometimes associated with grounding, stress relief, and reflecting negativity, though these are traditional beliefs and not scientific claims