igneous
Basalt with Quartz Infill
Basalt (Mafic Extrusive Volcanic Rock)
Hardness: 6-7 Mohs; Color: Dark grey to black matrix with white mineral inclusion; Luster: Dull/Earthy (matrix), Vitreous (inclusion); Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black matrix with white mineral inclusion
- Luster
- Dull/Earthy (matrix), Vitreous (inclusion)
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black matrix with white mineral inclusion; Luster: Dull/Earthy (matrix), Vitreous (inclusion); Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The white patch is likely a secondary mineral deposit (like quartz or calcite) that filled a vesicle or crack after the rock cooled.
Uses & applications
Commonly used as aggregate in construction, road base, and concrete. Small river-worn specimens are popular for aquarium decor or 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 extensively on the Moon and Mars.
Field identification & locations
Identify by its heavy weight, dark color, and fine-grained texture. To distinguish the white inclusion from calcite, a drop of vinegar can be used; if it bubbles, it is calcite; if not, it is likely quartz.
