igneous
Basalt River Stone
Aphanitic Mafic Igneous Rock
Hardness: 5-6 Mohs; Color: Dark grey to charcoal with greenish/brownish weathering; Luster: Dull/Earthy; Crystal structure: Fine-grained/aphanitic; Specific gravity: 2.8-3.0
- Hardness
- 5-6 Mohs
- Color
- Dark grey to charcoal with greenish/brownish weathering
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 Mohs; Color: Dark grey to charcoal with greenish/brownish weathering; Luster: Dull/Earthy; Crystal structure: Fine-grained/aphanitic; 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's surface. This specific specimen has been rounded by fluvial (river) or glacial transport over thousands of years.
Uses & applications
Used in construction as aggregate, road base, and railroad ballast. Smooth river stones are popular in landscaping, aquariums, and massage therapy (hot stones).
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 interior color, and fine-grained texture. Common in volcanic regions and riverbeds. Look for a smooth, water-worn exterior with occasional small pitting (vesicles).
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Dark Igneous Rock (Likely Basalt or Diabase)
Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.
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