metamorphic
Biotite Schist
Biotite Mica Schist
Hardness: 2.5-3; Color: Dark brown to black with sparkling/silvery flakes; Luster: Pearly to submetallic; Structure: Foliated with visible mica alignment; Cleavage: Perfect basal cleavage on individual mica flakes; Specific Gravity: 2.7-3.3
- Hardness
- 2
- Color
- Dark brown to black with sparkling/silvery flakes
- Luster
- Pearly to submetallic
Identified More metamorphic →
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Physical properties
Hardness: 2.5-3; Color: Dark brown to black with sparkling/silvery flakes; Luster: Pearly to submetallic; Structure: Foliated with visible mica alignment; Cleavage: Perfect basal cleavage on individual mica flakes; Specific Gravity: 2.7-3.3
Formation & geological history
Formed through the regional metamorphism of shale or mudstone at medium metamorphic grades (greenschist to amphibolite facies). The heat and pressure cause clay minerals to recrystallize into mica plates.
Uses & applications
Primarily of geological interest; used in construction as fill or decorative stone, and occasionally used in the manufacture of heat-resistant electrical insulators.
Geological facts
The high volume of mica flakes in schist produces a shimmering effect known as 'schistosity'. Biotite is known as 'black mica' due to its high iron and magnesium content.
Field identification & locations
Identify by its platy, foliated layers and the way it sparkles in sunlight. Found in mountain belts and areas with ancient continental crust. Collectors should look for garnets which are often found embedded within this rock.
