igneous
Basalt with Quartz Veining
Aphanitic Mafic Igneous Rock (primarily Plagioclase and Pyroxene)
Hardness: 5-6 (Basalt), 7 (Quartz inclusions); Color: Dark grey to black matrix with white/cream veins; Luster: Dull to earthy (matrix), vitreous (veins); Structure: Fine-grained/aphanitic; Specific Gravity: 2.8-3.0
- Hardness
- 5-6 (Basalt), 7 (Quartz inclusions)
- Color
- Dark grey to black matrix with white/cream veins
- Luster
- Dull to earthy (matrix), vitreous (veins)
Identified More igneous →
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Physical properties
Hardness: 5-6 (Basalt), 7 (Quartz inclusions); Color: Dark grey to black matrix with white/cream veins; Luster: Dull to earthy (matrix), vitreous (veins); Structure: Fine-grained/aphanitic; 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 light-colored veins formed later when silica-rich hydrothermal fluids filled fractures in the cooling rock.
Uses & applications
Basalt is used extensively in construction as aggregate for roads and railroad ballast. Veined specimens are often kept as decorative river stones or garden landscaping accents.
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 on the Moon and Mars.
Field identification & locations
Identify by its heavy weight, dark color, and fine texture. The white lines (veins) do not scratch with a steel knife, indicating quartz or a hard silicate. Commonly found in volcanic fields, riverbeds, and glacial till.
