igneous
Basalt
Basalt (principally Plagioclase Feldspar and Pyroxene)
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to earthy; Structure: Aphanitic (fine-grained), often vesicular or massive; Specific Gravity: 2.8–3.0.
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black
- Luster
- Dull to earthy
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to earthy; Structure: Aphanitic (fine-grained), often vesicular or massive; 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. Most specimens are from the Cenozoic era, though occurrences date back billions of years.
Uses & applications
Extensively used in construction as aggregate (crushed stone), for paving roads, railroad ballast, and in the production of stone wool insulation.
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 in the field by its dark color, heavy weight (density), and lack of visible crystals. It is found globally in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.
