igneous
Basalt with Quartz Veining
Amygdaloidal Basalt (predominately SiO2 and (Na,Ca)(Si,Al)4O8)
Hardness: 6-7 Mohs; Color: Dark grey to black with white/translucent veins; Luster: Dull to sub-vitreous; Crystal Structure: Aphanitic (fine-grained matrix); Cleavage: None (conchoidal fracture).
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black with white/translucent veins
- Luster
- Dull to sub-vitreous
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black with white/translucent veins; Luster: Dull to sub-vitreous; Crystal Structure: Aphanitic (fine-grained matrix); Cleavage: None (conchoidal fracture).
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near a planetary surface. The white veins are later hydrothermal secondary mineral infillings (quartz or calcite) deposited in fractures.
Uses & applications
Commonly used in construction as crushed stone, road base, and concrete aggregate. Occasional use in ornamental landscaping.
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 in abundance on the Moon and Mars.
Field identification & locations
Identify by its heavy weight, dark color, and fine-grained texture. To distinguish from surface staining, look for the 'vein' cutting through the rock body. Commonly found in volcanic fields and coastal outcrops.
