igneous
Tumbled reddish-brown volcanic rock, likely basalt or andesite
Fine-grained mafic to intermediate igneous rock; commonly plagioclase with pyroxene and/or olivine, possibly iron oxides
AI-generated identification · may be incorrectTypically Mohs 5–6, dark reddish-brown, dull to slightly waxy/glassy luster, very fine-grained and massive with no visible cleavage; the rounded shape indicates tumbling or water abrasion. Exact identification requires a fresh surface, streak, density, and magnification.
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Physical properties
Typically Mohs 5–6, dark reddish-brown, dull to slightly waxy/glassy luster, very fine-grained and massive with no visible cleavage; the rounded shape indicates tumbling or water abrasion. Exact identification requires a fresh surface, streak, density, and magnification.
Formation & geological history
Formed when lava cooled rapidly at or near Earth’s surface; reddish coloration commonly reflects oxidation of iron-bearing minerals during weathering. Volcanic rocks range from Precambrian to modern in age and occur widely in lava flows and volcanic terrains.
Uses & applications
Used as aggregate, roadstone, riprap, landscaping stone, and decorative tumbled material; generally not valuable as a gemstone.
Geological facts
The image alone cannot reliably distinguish basalt from andesite, iron-rich rhyolite, or another altered volcanic rock. Surface moisture or polish can intensify the dark red-brown appearance.
Field identification & locations
Look for a fine texture, high density, lack of layering, and possible tiny feldspar or dark mineral grains; basalt is usually more magnetic and darker, while andesite is commonly lighter. Common worldwide, especially volcanic regions.
