igneous
Polished dark pebble, likely basalt
Basalt; fine-grained mafic rock dominated by plagioclase and pyroxene, commonly with olivine
AI-generated identification · may be incorrectTypically dark gray to black, fine-grained, opaque, and dull to submetallic when polished; hardness about 6, no visible cleavage, and specific gravity roughly 2.8–3.0. The specimen’s rounded, glossy surface indicates tumbling or water wear.
Identified More igneous →
Explore Polished dark pebble, likely basalt in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically dark gray to black, fine-grained, opaque, and dull to submetallic when polished; hardness about 6, no visible cleavage, and specific gravity roughly 2.8–3.0. The specimen’s rounded, glossy surface indicates tumbling or water wear.
Formation & geological history
Basalt forms when low-silica, iron- and magnesium-rich lava rapidly cools at or near Earth’s surface, mainly in oceanic crust, volcanic fields, and flood-basalt provinces. Individual pieces may range from geologically young stream cobbles to ancient volcanic rocks.
Uses & applications
Used as aggregate, road stone, riprap, building stone, and occasionally for ornamental carvings or worry stones; this small polished piece has modest decorative value.
Geological facts
The image is consistent with basalt but cannot confirm composition without tests; similar dark pebbles may be andesite, diabase, slate, or industrial slag.
Field identification & locations
Look for uniformly fine texture, high density, black-gray color, and tiny pale plagioclase specks; a streak test is usually gray, and a magnet may show weak attraction if magnetite-rich. Common worldwide near volcanic regions and river gravels.
