igneous
Dark volcanic sand and basalt fragment
Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectThe specimen appears to be a small, dark gray-black, fine-grained basalt fragment surrounded by volcanic sand. Basalt has Mohs hardness about 5–6, dull to slightly vitreous luster, no cleavage in the rock mass, and specific gravity around 2.8–3.0; individual sand grains may include olivine or magnetite.
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Physical properties
The specimen appears to be a small, dark gray-black, fine-grained basalt fragment surrounded by volcanic sand. Basalt has Mohs hardness about 5–6, dull to slightly vitreous luster, no cleavage in the rock mass, and specific gravity around 2.8–3.0; individual sand grains may include olivine or magnetite.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, volcanic islands, and lava fields. Its age cannot be determined from the image; associated volcanic deposits may range from recent to billions of years old.
Uses & applications
Common basalt is used as crushed aggregate, road stone, railway ballast, riprap, and building stone; attractive polished pieces may be sold as lapidary specimens. Loose volcanic sand generally has little commercial value.
Geological facts
The greenish grains may be olivine, while very black grains may be magnetite or volcanic glass. A magnet test can indicate magnetite-rich material, and a fresh broken surface typically looks dark, compact, and fine-grained.
Field identification & locations
Likely locations include Hawaii, Iceland, the Canary Islands, oceanic seafloors, and continental volcanic regions. Identification is strengthened by a dark color, heavy feel, fine texture, and absence of visible large crystals; image-based identification remains approximate.
