metamorphic
Hornblende–biotite schist (probable)
Amphibole–mica schist; chiefly hornblende, biotite, quartz, and feldspar
AI-generated identification · may be incorrectDark gray to black, coarse-grained, strongly foliated and sparkly from aligned mica; irregular cleavage and crystalline texture. Typical hardness is about 5–6, with specific gravity roughly 2.8–3.2; rusty brown areas may be weathered iron-bearing minerals.
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Physical properties
Dark gray to black, coarse-grained, strongly foliated and sparkly from aligned mica; irregular cleavage and crystalline texture. Typical hardness is about 5–6, with specific gravity roughly 2.8–3.2; rusty brown areas may be weathered iron-bearing minerals.
Formation & geological history
Formed when basaltic or clay-rich protoliths underwent medium- to high-grade regional metamorphism, producing aligned amphibole and mica. Its precise geological age cannot be determined from the photograph and depends on locality.
Uses & applications
Used locally as crushed aggregate, riprap, or decorative stone; generally has limited gemstone value because it is tough but cleaves along foliation.
Geological facts
The specimen appears to contain conspicuous dark amphibole and reflective mica, possibly with quartz or feldspar. Exact identification would benefit from a fresh surface, streak, hardness tests, and thin-section or X-ray analysis.
Field identification & locations
Look for planar foliation, glittering aligned flakes, and dark amphibole prisms—features distinguishing schist from massive basalt or granite. Common in regional metamorphic belts worldwide, including the Appalachians, Alps, Scandinavia, and many Precambrian shields.
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