igneous
Basalt
Basalt (dominated by plagioclase feldspar and pyroxene)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull/Earthy
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specific specimen appears to be a water-worn river pebble or beach stone.
Uses & applications
Commonly used as aggregate in construction, road base, concrete, and as decorative landscaping 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 common on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture with no visible crystals to the naked eye. Frequently found near volcanic sites, coastal areas, or riverbeds downstream from volcanic zones.
