igneous
Basalt with Quartz/Calcite Veins
Amygdaloidal Basalt (SiO2 or CaCO3 inclusions)
Hardness: 6-7 (basalt matrix); Color: dark grey to black with white/cream veins; Luster: dull/matt matrix with vitreous veins; Crystal structure: fine-grained (aphanitic) matrix.
- Hardness
- 6-7 (basalt matrix)
- Color
- dark grey to black with white/cream veins
- Luster
- dull/matt matrix with vitreous veins
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Physical properties
Hardness: 6-7 (basalt matrix); Color: dark grey to black with white/cream veins; Luster: dull/matt matrix with vitreous veins; Crystal structure: fine-grained (aphanitic) matrix.
Formation & geological history
Formed from the rapid cooling of basaltic lava at the Earth's surface. The white veins are secondary mineralizations (usually quartz or calcite) deposited by hydrothermal fluids filling fractures and cracks long after the initial cooling.
Uses & applications
Common basalt is used in construction as road base, concrete aggregate, and railroad ballast. Veined specimens are often collected as decorative river/beach stones or for lapidary work.
Geological facts
Basalt is the most common rock in the Earth's crust and makes up most of the ocean floor. The white 'stripes' are geological records of seismic activity or stress that cracked the rock, which was then 'healed' by mineral-rich water.
Field identification & locations
Identify in the field by its heavy weight (high density), dark color, and high hardness (will scratch glass if it's quartz-veined). Commonly found on volcanic coastlines and riverbeds. For collectors, look for high contrast between the dark matrix and bright white veins.
