igneous
Rounded volcanic pebble
Likely basaltic-andesite or altered basalt; exact identification requires testing
AI-generated identification · may be incorrectDark brown-gray, fine-grained and weakly vesicular, with a dull to faintly vitreous luster and rounded beach-worn form. Likely hardness about 5–6 Mohs; cleavage absent and specific gravity roughly 2.7–3.0.
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Physical properties
Dark brown-gray, fine-grained and weakly vesicular, with a dull to faintly vitreous luster and rounded beach-worn form. Likely hardness about 5–6 Mohs; cleavage absent and specific gravity roughly 2.7–3.0.
Formation & geological history
An extrusive igneous rock formed when mafic to intermediate lava cooled rapidly, later rounded by wave abrasion and transported as beach gravel. Its precise geological age cannot be determined visually.
Uses & applications
Primarily a natural beach pebble or collector specimen; similar basalt is used as crushed aggregate, road stone, riprap, and occasionally landscaping material.
Geological facts
The reddish-brown surface likely reflects iron oxidation and weathering rather than the rock’s fresh interior color. Small pale grains may be feldspar or weathered vesicle fillings.
Field identification & locations
Common in volcanic coastal regions and glacial or river-derived gravel beaches. A fresh broken surface, streak, magnetism, and acid test can help distinguish basaltic rock from iron-rich sedimentary pebbles.
