igneous
Basalt with Quartz Vein
Basaltic rock with hydrothermal SiO2 filling
Hardness: 6-7 (Mohs scale), Color: Dark grey to black matrix with a white/translucent streak, Luster: Dull/earthy matrix with vitreous vein, Structure: Fine-grained aphanitic matrix
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Dark grey to black matrix with a white/translucent streak, Luster: Dull/earthy matrix with vitreous vein, Structure: Fine-grained aphanitic matrix
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The internal vein formed later as silica-rich fluids filled cooling fractures.
Uses & applications
Construction aggregate, road base, and decorative stone. Sometimes used in aquarium landscaping or as a teaching specimen for geological processes.
Geological facts
Basalt is the most common rock in Earth's crust and makes up most of the ocean floor. The white line through this rock is a 'history book' of a fracture that occurred long after the lava cooled.
Field identification & locations
Identify by its heavy weight (high specific gravity), dark color, and fine-grained texture. Look for similar specimens in volcanic fields, ancient lava flows, or as river-worn cobbles in many regions.
