metamorphic
Dark garnet-bearing metamorphic rock (probable garnet schist/amphibolite)
Garnet schist or garnet amphibolite; chiefly quartz, mica/amphibole, feldspar, and almandine–pyrope garnet
AI-generated identification · may be incorrectDark gray-green, fine- to medium-grained, dull to slightly vitreous surface with reddish-brown garnet-like patches. Typical hardness is about 6–7 overall; garnet is 6.5–7.5 Mohs, commonly without cleavage, with irregular fracture and specific gravity around 3.0–4.2.
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Physical properties
Dark gray-green, fine- to medium-grained, dull to slightly vitreous surface with reddish-brown garnet-like patches. Typical hardness is about 6–7 overall; garnet is 6.5–7.5 Mohs, commonly without cleavage, with irregular fracture and specific gravity around 3.0–4.2.
Formation & geological history
Formed when a basaltic or clay-rich protolith underwent moderate- to high-grade metamorphism during mountain building, generally hundreds of millions to billions of years ago. The image is insufficient to determine the exact mineral assemblage or age.
Uses & applications
Usually collected as a geological specimen or used locally as decorative stone; garnet-bearing material may be lapidary-cut, though this rough piece is unlikely to have high jewelry value.
Geological facts
Reddish areas may be garnet, but could also be iron-oxide staining or weathered sulfide; confirmation requires a fresh surface, hardness testing, and ideally microscopy or elemental analysis.
Field identification & locations
Look for visible red garnet grains, mica foliation, and a dense dark matrix; common in metamorphic belts worldwide, including India, Norway, the Alps, and the northeastern United States. Estimated value: about $5–$25 for a small common specimen, higher only if garnets are large and well formed.
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