igneous
Rounded green-gray river cobble
Likely altered basalt or andesite; exact identification requires a fresh surface and tests
AI-generated identification · may be incorrectFine-grained, massive, dull to weakly satin luster, green-gray color, and no visible cleavage or crystals; estimated Mohs hardness 5.5–7 and specific gravity about 2.7–3.1. The smooth rounded shape reflects prolonged water abrasion, not crystal form.
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Physical properties
Fine-grained, massive, dull to weakly satin luster, green-gray color, and no visible cleavage or crystals; estimated Mohs hardness 5.5–7 and specific gravity about 2.7–3.1. The smooth rounded shape reflects prolonged water abrasion, not crystal form.
Formation & geological history
Probably a weathered volcanic rock formed when basaltic-to-intermediate lava cooled rapidly, then altered by circulating fluids; age is indeterminate from the image. Its present shape likely formed in a river, beach, or glacial outwash environment.
Uses & applications
Commonly used as landscaping stone, garden cobble, drainage material, and decorative rock; generally little jewelry value unless unusually attractive or locally significant.
Geological facts
The green coloration may come from chlorite, epidote, actinolite, or weathering minerals. A streak, magnetism test, acid test, and examination of a broken face would improve identification.
Field identification & locations
Look for fine grain, high toughness, dark green-gray color, and absence of layering or obvious quartz. Common in volcanic terrains and stream deposits; avoid collecting where prohibited.
