igneous
Basalt
Basalt (dominated by plagioclase feldspar, pyroxene, and olivine)
Hardness: 6 (Mohs scale); Color: Dark gray to black, often with greenish hues; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0.
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black, often with greenish hues
- Luster
- Dull to sub-metallic
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray to black, often with greenish hues; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity magnesium-rich and iron-rich lava at or very near the Earth's surface. Extrusive volcanic rock found in oceanic crust and continental flood basalt provinces.
Uses & applications
Used extensively in construction as road base, concrete aggregate, and railroad ballast. Also used as dimension stone and for industrial floor tiles due to its durability.
Geological facts
Basalt is the most common rock type in the Earth's crust, making 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, dense, fine-grained appearance and heavy weight relative to its size. Can be found in volcanic regions, along riverbeds carrying volcanic sediment, and shorelines.
