igneous
Iron-rich weathered basalt (vesicular basalt)
Basalt, chiefly plagioclase feldspar and pyroxene with oxidized iron minerals
AI-generated identification · may be incorrectTypically dark gray to brown, fine-grained, locally vesicular, with dull to earthy luster; hardness about 5–6 Mohs and specific gravity roughly 2.8–3.1. The rusty coloration indicates surface oxidation, while the rounded shape suggests water or sediment abrasion.
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Physical properties
Typically dark gray to brown, fine-grained, locally vesicular, with dull to earthy luster; hardness about 5–6 Mohs and specific gravity roughly 2.8–3.1. The rusty coloration indicates surface oxidation, while the rounded shape suggests water or sediment abrasion.
Formation & geological history
A volcanic rock formed when mafic lava rapidly cooled at or near Earth’s surface; individual basalt flows range from recent to Precambrian in age. This specimen was likely weathered and transported in a stream, beach, or glacial deposit.
Uses & applications
Basalt is widely used as crushed aggregate, road stone, riprap, and building stone; attractive pieces may be sold as natural-history specimens. It is generally not suitable for jewelry unless polished as an ornamental stone.
Geological facts
Vesicles are gas bubbles preserved in cooling lava, and iron-bearing minerals commonly weather to orange-brown oxides such as limonite or hematite.
Field identification & locations
Identify it by its dense fine-grained texture, dark mafic minerals, possible small cavities, and weak or absent layering; a streak test is usually gray to brown, and it should not fizz strongly in dilute acid. Common worldwide in volcanic regions and river or beach gravels.
