igneous
Dark green-gray basalt (possibly metabasalt/greenstone)
Basalt; chiefly plagioclase feldspar and pyroxene, with possible chlorite/actinolite alteration
AI-generated identification · may be incorrectFine-grained, massive, dark gray-green, dull to faintly waxy luster, with thin rusty fractures from iron oxidation. Hardness about 6–6.5 Mohs; no visible cleavage; typically dense, with specific gravity around 2.8–3.1.
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Physical properties
Fine-grained, massive, dark gray-green, dull to faintly waxy luster, with thin rusty fractures from iron oxidation. Hardness about 6–6.5 Mohs; no visible cleavage; typically dense, with specific gravity around 2.8–3.1.
Formation & geological history
Likely an extrusive volcanic rock formed when basaltic lava cooled rapidly, generally in the Mesozoic or younger geologic record; the green tint may reflect later low-grade metamorphism or hydrothermal alteration.
Uses & applications
Used as aggregate, road base, riprap, paving stone, and occasionally as a polished decorative stone; this ordinary specimen has little jewelry value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and forms much of the oceanic crust. Its fine texture indicates cooling too rapidly for large crystals to develop.
Field identification & locations
Identify it by its uniform fine grain, dark color, high density, and lack of obvious quartz or large crystals; a streak, acid, and magnet test can help distinguish it from slate or serpentinite. Common worldwide, especially in volcanic regions and oceanic crust.
