igneous
Basalt Pebble
Extrusive mafic igneous rock (predominantly plagioclase feldspar and pyroxene)
AI-generated identification · may be incorrectHardness: 5.5 - 6.0 on Mohs scale; Color: dark grey to charcoal-black; Luster: dull to faintly waxy/silky when naturally smoothed or polished; Texture: fine-grained (aphanitic); Specific Gravity: 2.8 - 3.0
- Hardness
- 5
- Color
- dark grey to charcoal-black
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Physical properties
Hardness: 5.5 - 6.0 on Mohs scale; Color: dark grey to charcoal-black; Luster: dull to faintly waxy/silky when naturally smoothed or polished; Texture: fine-grained (aphanitic); Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling and crystallization of basaltic lava at or very near the Earth's surface, followed by prolonged mechanical weathering, tumbling, and rounding in high-energy fluvial (river) or coastal beach environments.
Uses & applications
Commonly used in hot stone massage therapy due to excellent heat retention, landscaping, water features, home decor, and historically for grinding tools or building material.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up almost all oceanic crust as well as extensive volcanic plateaus. The smooth, egg-like shape is achieved naturally through millions of wave or current tumbling cycles.
Field identification & locations
Identified in the field by its dense, fine-grained texture, dark uniform color, lack of visible large quartz grains, and heavy feel for its size. Frequently found along volcanic coastlines (e.g., Iceland, Hawaii, the Pacific Northwest) and volcanic riverbeds.
