igneous
Weathered basalt (likely altered basalt)
Basalt, chiefly plagioclase feldspar and pyroxene, with possible chlorite/epidote alteration
AI-generated identification · may be incorrectFine-grained, dark gray to purplish rock with dull luster, irregular fracture, and pale mineral-filled veins; typical hardness about 5–6 Mohs and specific gravity 2.8–3.1. The visible texture is too weathered and coarse-fractured for confident mineral identification.
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Physical properties
Fine-grained, dark gray to purplish rock with dull luster, irregular fracture, and pale mineral-filled veins; typical hardness about 5–6 Mohs and specific gravity 2.8–3.1. The visible texture is too weathered and coarse-fractured for confident mineral identification.
Formation & geological history
Basalt forms when low-silica mafic lava cools rapidly at or near Earth’s surface, commonly in volcanic fields, oceanic crust, and ancient lava flows. Its age cannot be determined from the photograph; pale veins likely formed later from circulating groundwater or hydrothermal fluids.
Uses & applications
Used as crushed aggregate, road stone, riprap, and occasionally building stone; unattractive hand specimens generally have little jewelry value.
Geological facts
Basalt is Earth’s most abundant volcanic rock and commonly weathers to iron-rich reddish or brown soils. Alteration can produce green chlorite, epidote, or secondary quartz and calcite.
Field identification & locations
Look for a dense, dark, fine-grained matrix, lack of obvious quartz, and possible tiny feldspar crystals; a streak, hardness, and acid test would help distinguish basalt from andesite or altered gabbro. Common in volcanic regions and ancient continental lava provinces.
