igneous
Basalt with Quartz Veins
Basalt (composition: SiO2, MgO, FeO, Al2O3, CaO)
Hardness: 6-7 Mohs; Color: Dark grey to black matrix with white silica veins; Luster: Dull/earthy (matrix) to vitreous (veins); Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black matrix with white silica veins
- Luster
- Dull/earthy (matrix) to vitreous (veins)
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black matrix with white silica veins; Luster: Dull/earthy (matrix) to vitreous (veins); 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 or very near the Earth's surface. The white veins represent secondary mineralization where hydrothermal fluids filled fractures in the rock long after the initial cooling.
Uses & applications
Used primarily in construction as crushed stone, concrete aggregate, and railroad ballast. Smooth river-worn specimens are often used for decorative landscaping or massage therapy stones.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up the majority of the ocean floor. It is also found extensively on the Moon and Mars.
Field identification & locations
Identify by its dark, dense, fine-grained texture and heavy feel for its size. Look for the 'cross-cut' white veins that do not match the main rock color. Commonly found on beaches, riverbeds, and volcanic fields.
