igneous
Rounded river stone, likely basaltic or volcanic rock
Fine-grained mafic volcanic rock, possibly basalt (exact identification requires testing)
AI-generated identification · may be incorrectDark gray-green, smooth and naturally polished, with a reddish-brown mineral vein or healed fracture. Likely hardness 5–6 Mohs, dull to faintly satin luster, very fine-grained and massive; cleavage absent and specific gravity approximately 2.8–3.1.
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Physical properties
Dark gray-green, smooth and naturally polished, with a reddish-brown mineral vein or healed fracture. Likely hardness 5–6 Mohs, dull to faintly satin luster, very fine-grained and massive; cleavage absent and specific gravity approximately 2.8–3.1.
Formation & geological history
Formed from rapidly cooled mafic lava, then rounded and smoothed by prolonged water transport; the red line may be iron-oxide staining along a fracture. Its precise geological age cannot be determined visually.
Uses & applications
Primarily a decorative or collectible stone, suitable for display, landscaping, and crafts; not normally valuable as jewelry material.
Geological facts
The oval shape and surface polish are characteristic of abrasion in a river or beach environment. A steel file or glass-scratch test, streak, magnetism, and a fresh broken surface would help distinguish basalt from metamorphic greenstone or other dark rocks.
Field identification & locations
Common in volcanic terrains and gravel beds worldwide, including the Pacific Northwest, Hawaii, Iceland, India, and ocean beaches. Look for uniformly fine texture, weak magnetism, and occasional tiny pale crystals; the vein is likely hematite-rich.
