igneous
Tumbled dark gray stone, likely basalt
Basalt; fine-grained mafic volcanic rock composed mainly of plagioclase feldspar and pyroxene, commonly with olivine
AI-generated identification · may be incorrectDark gray, matte to slightly granular luster, fine crystalline texture, and no visible cleavage; typical hardness is about 5–6 Mohs and specific gravity about 2.8–3.0. The rounded shape indicates tumbling or natural abrasion.
Identified More igneous →
Explore Tumbled dark gray stone, likely basalt in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray, matte to slightly granular luster, fine crystalline texture, and no visible cleavage; typical hardness is about 5–6 Mohs and specific gravity about 2.8–3.0. The rounded shape indicates tumbling or natural abrasion.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, volcanic islands, and continental lava flows. Individual pieces may range from recent volcanic material to rocks millions or billions of years old.
Uses & applications
Used as crushed aggregate, road base, railroad ballast, building stone, and landscaping material; attractive polished pieces are inexpensive curiosities. It is not generally used as a gemstone.
Geological facts
The specimen’s fine texture and uniform dark color are consistent with basalt, though image-only identification cannot exclude fine-grained gabbro, diabase, or dark metamorphic rock.
Field identification & locations
Look for a dense dark-gray body, tiny interlocking crystals, and occasional small vesicles or pale feldspar grains; a streak test is usually gray. Common sources include volcanic regions, river gravels, beaches, and commercial rock tumbling mixes.
