igneous
Basalt with Quartz Vein
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6-7 Mohs; Color: Dark grey to black matrix with a white/yellowish quartz vein; Luster: Dull/earthy matrix, vitreous vein; Structure: Fine-grained aphanitic; Cleavage: None.
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black matrix with a white/yellowish quartz vein
- Luster
- Dull/earthy matrix, vitreous vein
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black matrix with a white/yellowish quartz vein; Luster: Dull/earthy matrix, vitreous vein; Structure: Fine-grained aphanitic; Cleavage: None.
Formation & geological history
Basalt forms from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. The vein was formed later when hydrothermal fluids rich in silica circulated through fractures in the rock, depositing quartz as they cooled. These are common in volcanic regions and ocean floors.
Uses & applications
Raw basalt is widely used in construction as crushed stone for road base, concrete aggregate, and railroad ballast. Distinctive veined specimens are popular for aquarium decor, garden stones, and amateur rock collecting.
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 dark, heavy, fine-grained texture. The presence of a linear vein indicates secondary mineral deposition. Commonly found in riverbeds or coastal areas near ancient volcanic activity.
