igneous
Polished dark granitoid pebble
Likely basalt or fine-grained gabbro; chiefly plagioclase and pyroxene, possibly magnetite
AI-generated identification · may be incorrectHardness about 5.5–6.5 Mohs; dark gray to black, fine-grained, with a subtle satin to dull luster and no visible cleavage. The smooth rounded shape indicates natural water wear, possibly enhanced by polishing.
Identified More igneous →
Explore Polished dark granitoid pebble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness about 5.5–6.5 Mohs; dark gray to black, fine-grained, with a subtle satin to dull luster and no visible cleavage. The smooth rounded shape indicates natural water wear, possibly enhanced by polishing.
Formation & geological history
An igneous rock crystallized from mafic magma, likely during ancient volcanic or intrusive activity; its exact geological age cannot be determined visually. It was later transported and rounded in a stream, beach, or glacial environment.
Uses & applications
Commonly used as aggregate, riprap, paving stone, landscaping material, and decorative pebble; attractive pieces may be sold as worry stones or display specimens.
Geological facts
Basalt is the most abundant volcanic rock on Earth and commonly contains tiny crystals invisible without magnification. The silvery flecks may reflect plagioclase, pyroxene, or mica-like alteration minerals.
Field identification & locations
Identify it by its dark color, high density, fine texture, and lack of layering or obvious large crystals; a streak, magnetism, and acid tests can help distinguish basalt from gabbro or metamorphic rocks. Common in volcanic terrains and glacial or river gravels.
