igneous
Basalt with Calcite Veins
Basalt (Mafic Volcanic Rock)
Hardness: 5-6 (Mohs); Color: Dark grey to charcoal with white veins; Luster: Dull/Matte (basalt) to Vitreous (calcite); Crystal Structure: Fine-grained aphanitic matrix; Cleavage: None in basalt, rhombohedral in veins.
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to charcoal with white veins
- Luster
- Dull/Matte (basalt) to Vitreous (calcite)
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to charcoal with white veins; Luster: Dull/Matte (basalt) to Vitreous (calcite); Crystal Structure: Fine-grained aphanitic matrix; Cleavage: None in basalt, rhombohedral in veins.
Formation & geological history
Formed from rapid cooling of magnesium-rich and iron-rich lava. The white veins are typically calcite or quartz that precipitated from hydrothermal fluids filling fractures long after the rock solidified.
Uses & applications
Commonly used in construction as crushed stone, road base, or decorative garden stones. High-quality smooth river stones are used in massage therapy and landscaping.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. The white veins act as a geological 'history book,' showing where the rock cracked under tectonic stress.
Field identification & locations
Identify by its heavy weight (high density), dark color, and fine texture. The white veins will often react (fizz) with weak acid if they are calcite. Commonly found on beaches and in volcanic regions.
