metamorphic
Mica Schist (with Golden/Biotite inclusions)
K(Mg,Fe)3AlSi3O10(F,OH)2 (Biotite), KAl2(AlSi3O10)(F,OH)2 (Muscovite)
Hardness: 2-3 (Mohs scale), Color: Brownish-gold to silvery-grey, Luster: Vitreous to pearly, Crystal structure: Monoclinic (tabular/platy), Cleavage: Perfect basal cleavage leading to 'sheets', Specific gravity: 2.7–3.3.
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Physical properties
Hardness: 2-3 (Mohs scale), Color: Brownish-gold to silvery-grey, Luster: Vitreous to pearly, Crystal structure: Monoclinic (tabular/platy), Cleavage: Perfect basal cleavage leading to 'sheets', Specific gravity: 2.7–3.3.
Formation & geological history
Formed through the regional metamorphism of clay-rich sedimentary rocks (shales) or igneous rocks under medium-grade heat and pressure. Most specimens are from the Proterozoic or Paleozoic eras, found in the roots of ancient mountain chains.
Uses & applications
Used in industry for electrical insulation and ground fillers (drywall, paint). Used in construction for decorative slabs or landscaping. Low jewelry value, but highly collectible for teaching geology and mineralogy.
Geological facts
The term 'Schist' comes from the Greek word 'schistos,' meaning 'to split,' referring to how the rock easily flakes into thin layers. Mica was once used as window panes in old Russian stoves and called 'Muscovy-glass.'
Field identification & locations
Identify in the field by its distinct foliation (shimmering layers) and the ability to peel off tiny flakes with a fingernail or knife. Commonly found in metamorphic terrains like the Appalachian Mountains or the Alps.
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