igneous
Basalt (Crushed Stone Aggregate)
Mafic Volcanic Basalt (Major Minerals: Plagioclase Feldspar, Pyroxene, Olivine)
Hardness: 5-6 (Mohs scale); Color: Dark grey to black; Luster: Dull to earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0.
- Hardness
- 5-6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull to earthy
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark grey to black; Luster: Dull to 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 the Earth's surface. This specimen appears to be an aggregate embedded in concrete, which is common in modern infrastructure.
Uses & applications
Primary use as road base, railroad ballast, and concrete aggregate in construction over millions of tons annually.
Geological facts
Basalt is the most common rock type in Earth's crust and makes up most of the ocean floor. It is also found extensively on the Moon and Mars.
Field identification & locations
Identify in the field by its very dark color, heavy weight compared to other rocks of similar size, and lack of visible crystals to the naked eye. Often found in volcanic regions or as imported construction material.
