igneous
River Stone (likely Basalt or Greywacke)
Basalt (fine-grained mafic igneous rock)
Hardness: 6-7 on Mohs scale; Color: dark grey to black/greenish; Luster: dull to waxy when polished; Structure: microcrystalline; Specific Gravity: 2.8-3.0
- Hardness
- 6-7 on Mohs scale
- Color
- dark grey to black/greenish
- Luster
- dull to waxy when polished
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Physical properties
Hardness: 6-7 on Mohs scale; Color: dark grey to black/greenish; Luster: dull to waxy when polished; Structure: microcrystalline; Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth surface. This specific specimen has been smoothed by fluvial (river) erosion over thousands of years.
Uses & applications
Used in landscaping, construction aggregate, hot stone massage therapy, and as decorative garden elements.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Identify by its heavy weight relative to size, dark uniform color, and the smooth, rounded texture caused by water tumbling. Commonly found in riverbeds and coastal beaches.
