igneous
Dark, iron-stained rock; exact identification uncertain
Possibly a fine-grained mafic igneous rock (basalt or diabase); image alone is insufficient for a reliable species-level identification
AI-generated identification · may be incorrectRough, dark gray to black, with rusty brown weathering and no obvious crystals. Hardness, luster, cleavage, and density cannot be established visually; basalt is typically Mohs 6, fine-grained, and composed chiefly of plagioclase and pyroxene.
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Physical properties
Rough, dark gray to black, with rusty brown weathering and no obvious crystals. Hardness, luster, cleavage, and density cannot be established visually; basalt is typically Mohs 6, fine-grained, and composed chiefly of plagioclase and pyroxene.
Formation & geological history
If basalt or diabase, it formed when mafic magma cooled; basalt commonly cools at or near the surface, while diabase cools in shallow intrusions. No age or formation environment can be determined from the photo.
Uses & applications
Unidentified hand specimen; basalt and diabase are used as aggregate, paving stone, and construction materials.
Geological facts
The rusty patches may reflect weathering of iron-bearing minerals, but are not diagnostic of a particular rock.
Field identification & locations
Check for visible grains with a hand lens, streak, magnetism, and hardness; these tests and locality information are needed to distinguish basalt from other dark rocks. Common dark rocks occur worldwide.
