igneous
Basalt with Calcite Veins
Aphanitic mafic volcanic rock with CaCO3 inclusions
Hardness: 5-6 (basalt) / 3 (calcite veins); Color: Dark grey to black with white veining; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained) matrix; Cleavage: None in basalt, perfect rhombohedral in calcite.
- Hardness
- 5-6 (basalt) / 3 (calcite veins)
- Color
- Dark grey to black with white veining
- Luster
- Dull to sub-vitreous
Identified More igneous →
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Physical properties
Hardness: 5-6 (basalt) / 3 (calcite veins); Color: Dark grey to black with white veining; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained) matrix; Cleavage: None in basalt, perfect rhombohedral in calcite.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The white veins formed later as mineral-rich groundwater circulated through fractures in the rock, depositing carbonate minerals.
Uses & applications
Used primarily in construction as crushed stone, concrete aggregate, and railroad ballast. Small weathered pieces are common in decorative landscaping or as garden stones.
Geological facts
Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. It is also found in abundance on the Moon and Mars.
Field identification & locations
Identify in the field by its heavy weight, dark color, and fine texture. The white veins will react (fizz) if a small drop of diluted hydrochloric acid or strong vinegar is applied, confirming calcite.
