metamorphic
Biotite Schist
Biotite-rich Schist
Hardness (Mohs scale): 2.5-3; Color: Dark grey to black with shiny speckles; Luster: Pearly to submetallic; Structure: Foliated with visible mica flakes; Cleavage: Perfect basal cleavage in mica components.
- Color
- Dark grey to black with shiny speckles
- Luster
- Pearly to submetallic
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Physical properties
Hardness (Mohs scale): 2.5-3; Color: Dark grey to black with shiny speckles; Luster: Pearly to submetallic; Structure: Foliated with visible mica flakes; Cleavage: Perfect basal cleavage in mica components.
Formation & geological history
Formed through the regional metamorphism of clay-rich sedimentary rocks (pelites) or igneous rocks under moderate to high heat and pressure. This transformation occurs deep within the Earth's crust during mountain-building events.
Uses & applications
Used primarily as decorative landscaping stone, crushed aggregate in construction, or for educational geological specimens. The mica within can sometimes be used as a filler in paints or plastics.
Geological facts
The 'sparkly' appearance is due to high concentrations of biotite mica, which reflects light from its flat, sheet-like crystal faces. It is a key indicator of intermediate-grade metamorphism.
Field identification & locations
Identify in the field by its distinct foliation (layering) and the abundance of dark, shiny mica flakes that flake off easily with a fingernail. Found in mountain ranges and ancient shield regions.
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