igneous
Small dark-gray stone, likely basalt
Basalt (fine-grained mafic volcanic rock; commonly plagioclase, clinopyroxene, and iron-rich minerals)
AI-generated identification · may be incorrectDark gray, dull to faintly glassy, fine-grained, and rounded/tumbled; typical hardness is about 6 Mohs, with no visible cleavage and generally high density (about 2.8–3.0 g/cm³). The image is insufficient to confirm mineral grains or vesicles.
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Physical properties
Dark gray, dull to faintly glassy, fine-grained, and rounded/tumbled; typical hardness is about 6 Mohs, with no visible cleavage and generally high density (about 2.8–3.0 g/cm³). The image is insufficient to confirm mineral grains or vesicles.
Formation & geological history
Basalt forms when low-silica lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, volcanic islands, and flood-basalt provinces. Specimen age cannot be determined visually and may range from recent to billions of years.
Uses & applications
Used extensively as crushed aggregate, roadstone, railroad ballast, and construction stone; attractive polished pieces are sold as inexpensive curios or landscaping material.
Geological facts
Its dark color reflects abundant ferromagnesian minerals and relatively little quartz. A magnet may show weak attraction if the basalt contains magnetite.
Field identification & locations
Common worldwide, especially around volcanic regions and oceanic crust; identify with a streak test, hardness test, dense feel, and possible tiny crystals or vesicles. It could also be another dark rock or slag without testing.
