metamorphic
Garnet Gneiss or Mica Schist with Garnet
Almandine Garnet-bearing Gneiss
Hardness: 6.5-7.5 (garnets), 6-7 (matrix); Color: Tan/white matrix with dark reddish-brown circular inclusions; Luster: Vitreous to dull; Crystal structure: Isometric (garnets) in a foliated or granoblastic matrix.
- Hardness
- 6
- Color
- Tan/white matrix with dark reddish-brown circular inclusions
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6.5-7.5 (garnets), 6-7 (matrix); Color: Tan/white matrix with dark reddish-brown circular inclusions; Luster: Vitreous to dull; Crystal structure: Isometric (garnets) in a foliated or granoblastic matrix.
Formation & geological history
Formed under high-grade regional metamorphism of clay-rich sedimentary rocks or igneous protoliths. High pressure and temperature cause recrystallization and the growth of porphyroblasts like garnet.
Uses & applications
Large outcrops are used for crushed stone in construction; specimens are popular for educational purposes and mineral collecting. High-grade garnets are used as abrasives.
Geological facts
The dark spots are almandine garnets, which are the most common members of the garnet group. This specific specimen's rounded shape indicates it has been weathered by water or glacial action.
Field identification & locations
Identify in the field by the 'spotted' appearance of dark, hard, rounded crystals within a lighter, often banded or sparkly (micaceous) host rock. Commonly found in eroded mountain belts.
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