metamorphic
Garnet Schist
Almandine-Mica Schist
Hardness: 6.5-7.5 (garnets), 2-3 (mica matrix); Color: Silvery-gray matrix with deep red to brownish-red garnets; Luster: Vitreous to pearly (mica) and resinous (garnet); Structure: Foliated schistose texture with porphyroblastic garnets.
- Hardness
- 6
- Color
- Silvery-gray matrix with deep red to brownish-red garnets
- Luster
- Vitreous to pearly (mica) and resinous (garnet)
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Physical properties
Hardness: 6.5-7.5 (garnets), 2-3 (mica matrix); Color: Silvery-gray matrix with deep red to brownish-red garnets; Luster: Vitreous to pearly (mica) and resinous (garnet); Structure: Foliated schistose texture with porphyroblastic garnets.
Formation & geological history
Formed through regional metamorphism of clay-rich sedimentary rocks (pelites) such as shale or mudstone under medium-grade temperature and pressure conditions (amphibolite facies).
Uses & applications
Garnets are used as industrial abrasives (sandblasting, waterjet cutting) and as gemstones if transparent. Schist is occasionally used as decorative stone or fill.
Geological facts
The large, well-formed garnet crystals embedded in the schist matrix are known as porphyroblasts. They grow larger than the surrounding minerals during the metamorphic process.
Field identification & locations
Identify by the distinct 'sparkling' flaky mica layers and the presence of hard, dodecahedral red crystals. Common in mountain belts like the Appalachians or Alps. Look for foliated layers that split easily.
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