igneous
Rounded weathered pebble, likely basaltic or metamorphic
Indeterminate fine-grained mafic rock; possibly basalt or altered basalt
AI-generated identification · may be incorrectGray-brown, dull to weakly satin luster, fine-grained and compact, with no visible crystals or cleavage; estimated Mohs hardness 5–6 and specific gravity roughly 2.8–3.1. Its smooth oval shape indicates prolonged water or abrasion wear.
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Physical properties
Gray-brown, dull to weakly satin luster, fine-grained and compact, with no visible crystals or cleavage; estimated Mohs hardness 5–6 and specific gravity roughly 2.8–3.1. Its smooth oval shape indicates prolonged water or abrasion wear.
Formation & geological history
Most likely formed as a volcanic mafic rock from cooling lava, then chemically weathered and rounded in a river, beach, or glacial deposit; exact age and origin cannot be determined from the image. The pale streaks may represent alteration, weathering, or mineral veins.
Uses & applications
Common pebbles have little commercial value, but suitable basalt is used as aggregate, roadstone, riprap, and occasionally decorative stone; this specimen is mainly a souvenir or teaching sample.
Geological facts
The image does not show diagnostic crystals, vesicles, fossils, or layering, so identification is provisional. A streak, magnetism test, fresh break, and hardness test would help distinguish basalt from slate, quartzite, or other dark rocks.
Field identification & locations
Look for similar rounded gray-brown stones in streambeds, beaches, and glacial gravels worldwide; basalt may be weakly magnetic and commonly shows tiny dark grains on a fresh surface. Avoid destructive testing if it may be archaeological.
