igneous
Basalt with Quartz/Calcite Veins
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6 (matrix), 7 (veins); Color: Dark grey to black with white linear inclusions; Luster: Dull/earthy for the rock, vitreous for the veins; Structure: Fine-grained/aphanitic; Specific Gravity: 2.8 - 3.0
- Hardness
- 6 (matrix), 7 (veins)
- Color
- Dark grey to black with white linear inclusions
- Luster
- Dull/earthy for the rock, vitreous for the veins
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Physical properties
Hardness: 6 (matrix), 7 (veins); Color: Dark grey to black with white linear inclusions; Luster: Dull/earthy for the rock, vitreous for the veins; Structure: Fine-grained/aphanitic; Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the surface. The white veins are secondary hydrothermal deposits where minerals like quartz or calcite filled fractures in the rock long after initial cooling.
Uses & applications
Predominantly used as crushed stone for road base, concrete aggregate, and railroad ballast. Small water-worn specimens like this are often kept as part of beach-combing collections or used in rock tumblers.
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 extensively on the Moon and Mars.
Field identification & locations
Identify by its dark, dense matrix and heavy weight relative to size. Found globally in volcanic regions and on beaches where glacial or river transport has deposited them. Collectors look for the unique patterns created by 'X' or 'cross' shaped veins.
