metamorphic
Garnet Schist
Almandine-Mica Schist
Hardness: 6.5-7.5 (garnets) vs 2-3 (mica matrix); Color: Silver-grey matrix with reddish-brown crystals; Luster: Pearly to sub-metallic (matrix), Vitreous (garnets); Foliated texture; Specific Gravity: 2.8-4.3.
- Hardness
- 6
- Color
- Silver-grey matrix with reddish-brown crystals
- Luster
- Pearly to sub-metallic (matrix), Vitreous (garnets)
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Physical properties
Hardness: 6.5-7.5 (garnets) vs 2-3 (mica matrix); Color: Silver-grey matrix with reddish-brown crystals; Luster: Pearly to sub-metallic (matrix), Vitreous (garnets); Foliated texture; Specific Gravity: 2.8-4.3.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under high pressure and temperature. The garnets grow as porphyroblasts within the foliated mica-rich matrix.
Uses & applications
Predominantly used as a geological educational specimen. Industrial-grade garnets can be used as abrasives in waterjet cutting and sandblasting.
Geological facts
The garnets in these rocks are often 'almandine', the most common member of the garnet group. Schist is characterized by having more than 50% platy and elongated minerals.
Field identification & locations
Identify by looking for 'sparkly' or 'shimmery' layers (foliation) containing distinct, rounded, reddish crystals. Found in mountain ranges like the Appalachians, Alps, or Himalayas.
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