igneous
Tumbled blue-gray stone, likely basalt
Basalt (fine-grained mafic volcanic rock; chiefly plagioclase and pyroxene, commonly with magnetite)
AI-generated identification · may be incorrectDark blue-gray, mottled, dull to faintly vitreous luster; fine-grained and massive with no visible cleavage. Typical hardness is about 5–6 Mohs and specific gravity about 2.8–3.1.
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Physical properties
Dark blue-gray, mottled, dull to faintly vitreous luster; fine-grained and massive with no visible cleavage. Typical hardness is about 5–6 Mohs and specific gravity about 2.8–3.1.
Formation & geological history
Forms when basaltic lava cools rapidly at or near Earth’s surface, generally in volcanic fields, oceanic crust, and flood-basalt provinces. Basalt ranges from Archean to Recent in age; this rounded specimen was likely naturally water-worn and then polished or tumbled.
Uses & applications
Used as crushed stone, aggregate, road material, building stone, and occasionally decorative tile; attractive pieces are sold as inexpensive landscaping or metaphysical stones.
Geological facts
The blue coloration may reflect altered basalt, volcanic glass, or minor minerals such as chlorite, epidote, or sodalite; the photograph is insufficient for a definitive identification.
Field identification & locations
Identify by its heavy, fine-grained dark matrix, irregular mottling, and lack of large crystals; test hardness and streak, and inspect a fresh surface. Common worldwide, especially volcanic regions and river or beach gravels.
