igneous
Basalt (with possible weathered crust)
Basalt (composition: Plagioclase feldspar, Pyroxene, Olivine)
Hardness: 5-6 (Mohs scale), Color: Dark grey to black with light brown surface weathering, Luster: Dull/Earthy, Crystal structure: Aphanitic (fine-grained), Specific gravity: 2.8-3.0
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Physical properties
Hardness: 5-6 (Mohs scale), Color: Dark grey to black with light brown surface weathering, 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 exposed at or very near the Earth's surface. This piece likely comes from a volcanic flow or dike.
Uses & applications
Commonly used in construction as crushed stone for road base, concrete aggregate, and railroad ballast. Fine specimens are used for decorative landscaping or geological collections.
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 on the Moon, Mars, and Venus.
Field identification & locations
Identify by its dark color, heavy weight (density), and lack of visible large crystals. Look for vesicular (pitted) textures or smooth, weathered exteriors in volcanic regions.
