igneous
Black Beach Pebble (Basalt/Greywacke Pebble)
Aphanitic Mafic Igneous Rock / Basalt
Hardness: 5.5 to 6.0 Mohs. Color: Dark grey to charcoal black with sub-metallic or matte sheen. Luster: Dull to satin/sub-metallic when polished or wet. Texture: Smooth, water-worn fine-grained (aphanitic) matrix. Specific Gravity: ~2.8-3.0.
- Hardness
- 5
- Color
- Dark grey to charcoal black with sub-metallic or matte sheen
- Luster
- Dull to satin/sub-metallic when polished or wet
Identified More igneous →
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Physical properties
Hardness: 5.5 to 6.0 Mohs. Color: Dark grey to charcoal black with sub-metallic or matte sheen. Luster: Dull to satin/sub-metallic when polished or wet. Texture: Smooth, water-worn fine-grained (aphanitic) matrix. Specific Gravity: ~2.8-3.0.
Formation & geological history
Formed as rapid-cooling lava flows (basalt) or fine-grained sedimentary rock, which was subsequently eroded, rounded, and polished over time by wave or stream action in riverbeds or coastal environments.
Uses & applications
Used extensively in landscaping, aquascaping, decorative stone arrangements, massage therapy (hot stones), and general rock collecting.
Geological facts
Smooth dark river and beach pebbles gain their rounded shape through thousands of years of natural attrition caused by water currents rolling them against sand and other stones.
Field identification & locations
Identify by its smooth rounded bean-like shape, dark uniform fine-grained matrix, and lack of visible large crystals. Extremely common along river banks, coastlines, and in landscaping gravel supplies worldwide.
