igneous
Basalt River Pebble
Aphanitic Mafic Volcanic Rock
Hardness: 5-6 Mohs. Color: Dark grey to charcoal. Luster: Dull/Earthy (weathered). Crystal structure: Microcrystalline (aphanitic). Cleavage: None. Specific gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- Dark grey to charcoal
- Luster
- Dull/Earthy (weathered)
Identified More igneous →
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Physical properties
Hardness: 5-6 Mohs. Color: Dark grey to charcoal. Luster: Dull/Earthy (weathered). Crystal structure: Microcrystalline (aphanitic). Cleavage: None. 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 specimen has been rounded and smoothed by fluvial (river) erosion over a long period.
Uses & applications
Commonly used as aggregate in construction, road base, or as decorative landscaping stones and garden mulch.
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 dark color, heavy weight for its size, and lack of visible crystals. Commonly found in riverbeds, volcanic regions, and coastal areas.
