metamorphic
Garnet-bearing metamorphic rock
Likely garnet schist or garnet amphibolite; garnet is commonly almandine, Fe₃Al₂(SiO₄)₃
AI-generated identification · may be incorrectDark brown-black, coarse and irregular, with reddish-brown garnet-like patches and a subdued vitreous to earthy luster. Garnet hardness is about 6.5–7.5 Mohs; the matrix is likely mica- or amphibole-rich and may show foliation.
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Physical properties
Dark brown-black, coarse and irregular, with reddish-brown garnet-like patches and a subdued vitreous to earthy luster. Garnet hardness is about 6.5–7.5 Mohs; the matrix is likely mica- or amphibole-rich and may show foliation.
Formation & geological history
Formed when a clay- or basalt-rich protolith underwent moderate- to high-grade metamorphism during mountain building. Such rocks commonly formed from Paleozoic to Precambrian crust, though age cannot be determined from the image.
Uses & applications
Used mainly as a decorative or teaching specimen; garnet may be extracted abrasively, while intact rock has limited construction value.
Geological facts
Garnet crystals are typically nonmetallic and lack cleavage, often breaking with uneven fractures. The dark matrix may contain biotite, hornblende, quartz, and feldspar.
Field identification & locations
Look for distinct reddish-brown, rounded garnet grains embedded in a foliated dark matrix; a hand lens and hardness/streak tests would help confirm it. Common in metamorphic belts worldwide, including the Appalachians, Scandinavia, and western North America.
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