igneous
Basalt with Quartz Veining
Basalt (Mafic Volcanic Rock with SiO2)
Hardness: 6-7 (Mohs scale), Color: Dark grey to black with white veins, Luster: Dull/Matte (matrix) to Vitreous (veins), Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific gravity: 2.8-3.0
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Dark grey to black with white veins, Luster: Dull/Matte (matrix) to Vitreous (veins), Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava. The white veins are secondary hydrothermal deposits where silica-rich fluids filled fractures in the rock long after initial cooling.
Uses & applications
Commonly used as crushed stone for road base, concrete aggregate, and railroad ballast. Smooth river-worn specimens are often used in landscaping and aquarium decor.
Geological facts
Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. The white 'lightning' patterns are actually fractures that healed over millions of years.
Field identification & locations
Identify by its heavy weight, dark fine-grained matrix, and the presence of hard white veins that cannot be scratched by a steel nail. Commonly found in volcanic regions or as glacial till and river cobbles.
