igneous
River Stone (likely Basalt or Diabase)
Mafic Igneous Rock (likely Basalt)
Hardness: 6-7 Mohs; Color: Dark grey to greenish-black with weathered tan/brown patina; Luster: Dull or earthy when weathered; Structure: Fine-grained (aphanitic); Cleavage: None/conchoidal; Shape: Well-rounded (sub-spherical).
- Hardness
- 6-7 Mohs
- Color
- Dark grey to greenish-black with weathered tan/brown patina
- Luster
- Dull or earthy when weathered
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to greenish-black with weathered tan/brown patina; Luster: Dull or earthy when weathered; Structure: Fine-grained (aphanitic); Cleavage: None/conchoidal; Shape: Well-rounded (sub-spherical).
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The rounded shape is the result of mechanical weathering and high-energy water transport in a river, stream, or glacial environment over thousands of years.
Uses & applications
Commonly used in landscaping, as drainage aggregate, in construction (crushed stone), for stone massage therapy (due to high heat retention), and as decorative garden accents.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floors. River stones are often referred to as 'cobbles' based on their size (64 to 256 mm).
Field identification & locations
Identified by its heavy weight, dark interior (if chipped), and smooth, rounded surface. Look for these in riverbeds, glacial till, or coastal beaches. They are excellent for testing the power of erosion.
