igneous
Basalt (with Iron Staining)
Mafic Igneous Rock
Hardness: 6 (Mohs); Color: Dark grey to black, weathered to rusty brown; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0.
- Hardness
- 6 (Mohs)
- Color
- Dark grey to black, weathered to rusty brown
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6 (Mohs); Color: Dark grey to black, weathered to rusty brown; 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 at the earth's surface. This specimen shows oxidation (rusting) due to exposure to moisture and oxygen.
Uses & applications
Commonly used as crushed stone for road base, concrete aggregate, railroad ballast, and in some architectural stone applications.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is similar in composition to rocks found on the Moon and Mars.
Field identification & locations
Identify by its heavy weight, dark interior, and fine-grained texture. It is often found in volcanic regions or as glacial erratic. Collectors look for vesicles or crystal inclusions like olivine.
