metamorphic
Schist with Biotite and Quartz
Biotite-Quartz Schist (Fe,Mg,Al silicate mix)
Hardness: 2.5-3 (biotite portions) to 7 (quartz portions); Color: Black, dark green, and tan/white; Luster: Pearly to vitreous; Structure: Foliated/Crystalline; Cleavage: Perfect basal on mica grains.
- Hardness
- 2
- Color
- Black, dark green, and tan/white
- Luster
- Pearly to vitreous
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Physical properties
Hardness: 2.5-3 (biotite portions) to 7 (quartz portions); Color: Black, dark green, and tan/white; Luster: Pearly to vitreous; Structure: Foliated/Crystalline; Cleavage: Perfect basal on mica grains.
Formation & geological history
Formed from the regional metamorphism of shale or mudstone under medium-to-high pressure and temperature conditions, typical of mountain-building events. Geological age varies by location, often Precambrian to Paleozoic.
Uses & applications
Used primarily as decorative stone, in garden landscaping, or as geological study specimens. Large-scale schist may be used for flagstone in construction.
Geological facts
This specimen shows a clear relationship between different metamorphic minerals; the dark 'book' of biotite mica is embedded in a matrix of quartz and feldspar, demonstrating the recrystallization of minerals during tectonic shifts.
Field identification & locations
Identify in the field by its distinct layering (schistosity) and the presence of shiny, flat mineral flakes. Commonly found in metamorphic belts like the Appalachians or the Alps. Look for the 'glitter' effect when held to light.
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