igneous
Basalt River Stone
Basalt (Aphanitic Mafic Volcanic Rock)
Hardness: 5 to 6 on Mohs scale; Color: dark gray to black, turning brownish when weathered; Luster: dull to earthy; Crystal Structure: fine-grained (aphanitic) or glassy due to rapid cooling; Cleavage: none, usually breaks with a conchoidal fracture.
- Hardness
- 5 to 6 on Mohs scale
- Color
- dark gray to black, turning brownish when weathered
- Luster
- dull to earthy
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Physical properties
Hardness: 5 to 6 on Mohs scale; Color: dark gray to black, turning brownish when weathered; Luster: dull to earthy; Crystal Structure: fine-grained (aphanitic) or glassy due to rapid cooling; Cleavage: none, usually breaks with a conchoidal fracture.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. This specific specimen shows rounding and smoothing characteristic of transport in a high-energy aquatic environment, such as a river or stream, over hundreds to thousands of years.
Uses & applications
Commonly used as aggregate in construction, road base, or railroad ballast. Polished versions are used for hot stone massage therapy and decorative landscaping.
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 extensively on the Moon and Mars.
Field identification & locations
Identified by its heavy weight (high density), dark color, and fine-grained texture with no visible crystals. Often found in volcanic regions or in riverbeds downstream from volcanic sources. Collectors value smooth, symmetrical 'worry stones' like this for tactile use.
