igneous
Weathered brown rock fragment
Likely altered basalt or andesite; precise identification is uncertain from the image
AI-generated identification · may be incorrectDark brown to gray, fine- to medium-grained, dull to weakly earthy luster, irregular fracture, and no visible cleavage; typical hardness approximately 5–6 Mohs and specific gravity about 2.7–3.1.
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Physical properties
Dark brown to gray, fine- to medium-grained, dull to weakly earthy luster, irregular fracture, and no visible cleavage; typical hardness approximately 5–6 Mohs and specific gravity about 2.7–3.1.
Formation & geological history
Probably a volcanic rock formed when lava cooled at or near Earth’s surface, later chemically weathered; its exact geological age and alteration history cannot be determined visually.
Uses & applications
Common volcanic rock is used as aggregate, road stone, riprap, and occasionally as a lapidary or teaching specimen; this small weathered fragment has negligible commercial value.
Geological facts
The rounded edges and mottled brown coloration indicate weathering, possibly involving iron-oxide staining. A fresh broken surface would provide a more reliable identification than the weathered exterior.
Field identification & locations
Common in volcanic terrains worldwide, including Iceland, the western United States, Mexico, India, and oceanic islands. Test for a fine crystalline texture, lack of fizz with dilute hydrochloric acid, and possible attraction to a magnet if basaltic.
