igneous
Basalt with Quartz Veining
Mafic Volcanic Rock with Silicate Micro-veins
Hardness: 5-7 (Mohs); Color: Dark grey to greenish-black matrix with white quartz veins; Luster: Dull or earthy (matrix), Vitreous (veins); Structure: Aphanitic (fine-grained) matrix; Specific Gravity: 2.8-3.0
- Hardness
- 5-7 (Mohs)
- Color
- Dark grey to greenish-black matrix with white quartz veins
- Luster
- Dull or earthy (matrix), Vitreous (veins)
Identified More igneous →
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Physical properties
Hardness: 5-7 (Mohs); Color: Dark grey to greenish-black matrix with white quartz veins; Luster: Dull or earthy (matrix), Vitreous (veins); Structure: Aphanitic (fine-grained) matrix; Specific Gravity: 2.8-3.0
Formation & geological history
Formed from molten lava that cooled rapidly near the Earth's surface. The white veins represent later secondary mineralization where silica-rich fluids filled cooling cracks or fractures in the rock, typically under hydrothermal conditions.
Uses & applications
Common basalt is used in construction (crushed stone, road base) and landscaping. River-worn specimens like this are popular for aquarium decor, garden stones, or as amateur pocket stones.
Geological facts
Basalt makes up more than 90% of all volcanic rock on Earth and also makes up the majority of the lunar mare on the Moon. The white quartz veins are often harder than the surrounding basalt and can stand out in relief after long periods of erosion.
Field identification & locations
Identify by its dark, dense matrix and fine grain. In the field, look for these along riverbeds or coastlines where water has tumbled the rock into a smooth, rounded cobble. Common in volcanic regions like the Pacific Northwest or Iceland.
