metamorphic
Mica Schist
Mica Schist (primarily Muscovite or Biotite sheet silicates)
Hardness: 2-3 (Mica) 6-7 (Quartz content); Color: Silvery-gold, brassy, or grey; Luster: Pearly to metallic (vitreous); Crystal Structure: Monoclinic; Cleavage: Perfect basal cleavage in mica flakes; SG: 2.7-2.8.
- Hardness
- 2-3 (Mica) 6-7 (Quartz content)
- Color
- Silvery-gold, brassy, or grey
- Luster
- Pearly to metallic (vitreous)
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Physical properties
Hardness: 2-3 (Mica) 6-7 (Quartz content); Color: Silvery-gold, brassy, or grey; Luster: Pearly to metallic (vitreous); Crystal Structure: Monoclinic; Cleavage: Perfect basal cleavage in mica flakes; SG: 2.7-2.8.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under intermediate to high temperatures and pressures. Over geological time (Proterozoic to Phanerozoic), the clay minerals transform into planar mica crystals.
Uses & applications
Used historically as a building stone (facing) and in some industrial lubricants. In modern times, it is primarily a landscape stone, an source of flake mica for paints/cosmetics, or a teaching specimen for geology.
Geological facts
The word 'schist' is derived from the Greek word 'schistos', meaning 'split', referring to the ease with which the rock can be cleaved into thin plates. It is the characteristic rock of many mountain belts.
Field identification & locations
Identify by 'schistosity'—the alignment of shimmering mica flakes that cause the rock to sparkle in the sun. It is common in metamorphic terrains like the Appalachian Mountains or the Alps. Fragments are often found in riverbeds downstream from metamorphic outcrops.
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