Mica-rich Schist
Biotite-Muscovite Schist · Mineral Specimen / Metamorphic Rock Component
Crystal System
Monoclinic; crystals are typically platy or foliated (micaceous habit), forming dense, shimmering aggregates.
Mineral Group
Silicates (Phyllosilicates / Mica Group)
Chemical Formula
K(Mg,Fe)3(AlSi3O10)(OH)2 [Biotite] / KAl2(AlSi3O10)(OH)2 [Muscovite]
Formation Process
Metamorphic; formed from high-pressure and medium-temperature transformation of pelitic (clay-rich) rocks like shale.
About This Crystal
A medium-grained metamorphic rock with a highly reflective, shimmering surface due to the parallel alignment of mica flakes. It appears granular with a silvery-grey to brownish metallic luster and is opaque to translucent in thin flakes.
Physical Characteristics
Color: Silvery-grey to bronze; Streak: White to pale grey; Cleavage: Perfect basal cleavage in individual grains; SG: 2.7-3.1; Fracture: Splintery/Uneven; Fluorescence: Generally none.
Optical Properties
Biotite and muscovite are doubly refractive with high birefringence, though usually observed as a 'schistose' shimmer rather than faceted optics.
Hardness & Durability
Origin Region
Widespread globally in metamorphic belts; notably Brazil, India, Russia, and the Appalachian Mountains (USA).
Hardness & Durability
Mohs Hardness 2.0–3.0 for mica components. Very brittle and prone to flaking or 'shedding' along foliation planes; low durability for jewelry.
Care & Maintenance
Avoid ultrasonic cleaners and water immersion which can cause delamination. Clean with a dry, soft brush. Store in a stable environment away from physical abrasion.
Rarity & Value
Common; primarily valued as geological specimens or decorative stone. Low commercial value compared to gemstones, typically $5-$30 for hand samples.
Special Characteristics
Exhibits strong schistosity; the parallel orientation of mineral grains creates a distinctive 'sparkle' or 'phyllitic sheen' when moved under light.
Lore & History
Historically used in windows (muscovy-glass) before glass was common. In lore, it is believed to help with mental clarity and shielding against negativity.