metamorphic
Biotite Schist with Garnet
Garnet-Biotite Schist
Hardness: 2.5-3 (biotite), 6.5-7.5 (garnet); Color: Black or dark brown with reddish inclusions; Luster: Pearly to submetallic; Crystal Structure: Monoclinic (biotite), Isometric (garnet); Cleavage: Perfect basal.
- Hardness
- 2
- Color
- Black or dark brown with reddish inclusions
- Luster
- Pearly to submetallic
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Physical properties
Hardness: 2.5-3 (biotite), 6.5-7.5 (garnet); Color: Black or dark brown with reddish inclusions; Luster: Pearly to submetallic; Crystal Structure: Monoclinic (biotite), Isometric (garnet); Cleavage: Perfect basal.
Formation & geological history
Formed through the regional metamorphism of clay-rich sedimentary rocks (shales) under high temperature and pressure conditions, typically during mountain-building events.
Uses & applications
Primarily used as a geological teaching specimen or for mineral collecting; schist is sometimes used in construction for fill or decorative garden stones.
Geological facts
Schist is characterized by its foliation, meaning its minerals are aligned in layers. The shiny black flakes are biotite mica, which allows the rock to split into thin sheets.
Field identification & locations
Identify by looking for flaky, shiny black mica surfaces (schistosity) and small, hard reddish-brown granular crystals (garnets). Found globally in metamorphic belts like the Appalachians or the Alps.
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