igneous
Weathered Basalt
Mafic Igneous Rock (primarily Plagioclase and Pyroxene)
Hardness: 5-6 Mohs. Color: Gray, dark green, or black, often weathering to brown or rusty orange. Luster: Dull to earthy. Structure: Fine-grained (aphanitic). Cleavage: Poor.
- Hardness
- 5-6 Mohs
- Luster
- Dull to earthy
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Physical properties
Hardness: 5-6 Mohs. Color: Gray, dark green, or black, often weathering to brown or rusty orange. Luster: Dull to earthy. Structure: Fine-grained (aphanitic). Cleavage: Poor.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specimen shows significant rounding and surface oxidation, likely from fluvial (river) transport.
Uses & applications
Used extensively in construction as aggregate for concrete and asphalt, railroad ballast, and occasionally for high-durability floor tiles or stone carvings.
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 by its heavy weight (high specific gravity), dark interior color when broken, and lack of visible crystals. Commonly found in volcanic fields, riverbeds, and coastal areas.
