metamorphic
Garnet-Bearing Gneiss
Garnetiferous Feldspathic Gneiss
Hardness: 6-7.5 (depending on garnet content); Color: Mottled grey, white, and tan with reddish-pink garnet inclusions; Luster: Vitreous to dull; Structure: Foliated or banded; Cleavage: None (garnets break conchoidally).
- Hardness
- 6-7
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7.5 (depending on garnet content); Color: Mottled grey, white, and tan with reddish-pink garnet inclusions; Luster: Vitreous to dull; Structure: Foliated or banded; Cleavage: None (garnets break conchoidally).
Formation & geological history
Formed through high-grade regional metamorphism of pro-liths (likely sedimentary shale or igneous granite) under intense heat and pressure, often during mountain-building events (orogeny) hundreds of millions of years ago.
Uses & applications
Primarily used as decorative stone, crushed stone for construction, and in some cases, the garnets are extracted for use as industrial abrasives or low-grade gemstones.
Geological facts
Gneiss is one of the most common rocks in the Earth's continental crust. Garnets within gneiss are often an indicator of the specific temperature and pressure conditions the rock underwent during formation.
Field identification & locations
Identify by looking for distinct mineral banding (foliation) and small, round, red-to-pink crystalline inclusions. Common in Precambrian shield areas like the Adirondack Mountains or the Canadian Shield.
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