igneous
Tumbled dark stone, likely basalt or slate
Basalt (fine-grained plagioclase–pyroxene rock), possibly slate/phyllite
AI-generated identification · may be incorrectSmooth, rounded, dark blue-gray to black, matte-to-waxy luster, very fine-grained and lacking visible crystals; apparent Mohs hardness about 5–7. The straight pale line may be a natural vein, fracture, or surface scratch.
Identified More igneous →
Explore Tumbled dark stone, likely basalt or slate in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Smooth, rounded, dark blue-gray to black, matte-to-waxy luster, very fine-grained and lacking visible crystals; apparent Mohs hardness about 5–7. The straight pale line may be a natural vein, fracture, or surface scratch.
Formation & geological history
If basalt, it formed from rapidly cooled mafic lava, commonly in oceanic crust and volcanic regions; if slate/phyllite, it formed by low-grade metamorphism of shale. Exact age and identification require fresh surface, hardness, and streak tests.
Uses & applications
Commonly sold as a worry stone, tumbled landscaping stone, or decorative specimen; basalt is used for aggregate and construction, while slate is used for roofing and architectural finishes.
Geological facts
The shape and polish indicate human tumbling, but processing does not exclude geological origin. Color alone cannot reliably distinguish basalt from dark metamorphic rocks.
Field identification & locations
Test an inconspicuous area: basalt commonly scratches glass weakly or not at all and has a gray streak; slate tends to show planar cleavage. Common sources include volcanic regions worldwide and slate belts.
