igneous
Tumbled dark stone, likely basalt
Basalt; primarily plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectFine-grained, dark gray-brown, opaque, and dull to subtly waxy from polishing; typical hardness is about 5–6 Mohs, with no visible cleavage and specific gravity around 2.8–3.0. The smooth, rounded form indicates tumbling or water wear.
Identified More igneous →
Explore Tumbled dark stone, likely basalt in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Fine-grained, dark gray-brown, opaque, and dull to subtly waxy from polishing; typical hardness is about 5–6 Mohs, with no visible cleavage and specific gravity around 2.8–3.0. The smooth, rounded form indicates tumbling or water wear.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic fields and oceanic crust; most examples are geologically young, though basalt occurs from Archean to present. The photograph cannot confirm composition, and a dark chert or other stone is also possible.
Uses & applications
Used as aggregate, road stone, building material, landscaping stone, and inexpensive polished decorative material. Small tumbled pieces generally have minimal gem value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. Its dark color reflects abundant iron- and magnesium-rich minerals.
Field identification & locations
Look for a uniformly fine texture, dark color, heavy feel, and possible tiny crystals or vesicles; a streak test is usually gray, and acid produces no reaction. Common worldwide, especially volcanic regions and river gravels.
