igneous
Fine-grained mafic rock, likely basalt or altered basalt
Basalt; chiefly plagioclase feldspar and pyroxene, with possible chlorite/serpentine alteration
AI-generated identification · may be incorrectDark greenish-gray, dull to slightly granular, and very fine-grained; individual crystals are difficult to see. Estimated Mohs hardness 5–6, with no obvious cleavage; the green color may indicate secondary alteration minerals.
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Physical properties
Dark greenish-gray, dull to slightly granular, and very fine-grained; individual crystals are difficult to see. Estimated Mohs hardness 5–6, with no obvious cleavage; the green color may indicate secondary alteration minerals.
Formation & geological history
Likely formed from rapidly cooled mafic lava, commonly in oceanic crust or volcanic terrains; alteration by hydrothermal fluids can produce the green tint. Exact age and identification cannot be established from the photograph alone.
Uses & applications
Basalt is used as crushed aggregate, road stone, concrete filler, and occasionally dimension stone; small specimens have modest collecting interest.
Geological facts
Greenstone-like color may reflect chlorite, epidote, or serpentine replacing original basalt minerals. A fresh broken surface and a hand lens would help distinguish basalt from schist, serpentinite, or slag.
Field identification & locations
Look for a dense, fine-grained texture, dark color, and strong weight relative to size; basalt commonly occurs in lava flows and volcanic mountains. It may be weakly magnetic if iron-bearing minerals are present.
