metamorphic
Garnet-Bearing Schist
Almandine Garnet Schist
Hardness: 6.5-7.5 (garnet) and 5.5-6 (schist matrix); Color: Gray to silver matrix with reddish-brown almandine crystals; Luster: Pearly to submetallic (mica) and vitreous (garnet); Crystal Structure: Isometric (garnet); Cleavage: Distinct in one direction (foliation).
- Hardness
- 6
- Color
- Gray to silver matrix with reddish-brown almandine crystals
- Luster
- Pearly to submetallic (mica) and vitreous (garnet)
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Physical properties
Hardness: 6.5-7.5 (garnet) and 5.5-6 (schist matrix); Color: Gray to silver matrix with reddish-brown almandine crystals; Luster: Pearly to submetallic (mica) and vitreous (garnet); Crystal Structure: Isometric (garnet); Cleavage: Distinct in one direction (foliation).
Formation & geological history
Forms through regional metamorphism of clay-rich sedimentary rocks (shales) under medium to high pressure and temperature. This process aligns micas to create the schistose texture.
Uses & applications
Large garnets are used as gemstones or abrasives. The rock itself is used in decorative landscaping and as an indicator of metamorphic grade for geological mapping.
Geological facts
The almandine garnets in this rock are often more resistant to weathering than the surrounding mica, causing them to protrude or 'pop out' from the surface.
Field identification & locations
Identify in the field by looking for a platy or flaky silver/gray rock containing round, dark red or brown protruding crystals. Commonly found in mountain ranges such as the Appalachians or the Alps.
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