igneous
Basalt with Quartz/Calcite Inclusions
Mafic Volcanic Rock (Fe-Mg silicate rich)
Hardness: 5-6 Mohs for matrix, 7 for quartz; Color: Dark grey to black with white patches; Luster: Dull/earthy matrix, vitreous inclusions; Crystal structure: Aphanitic (fine-grained) matrix; Density: High (2.8–3.0 g/cm3).
- Hardness
- 5-6 Mohs for matrix, 7 for quartz
- Color
- Dark grey to black with white patches
- Luster
- Dull/earthy matrix, vitreous inclusions
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Physical properties
Hardness: 5-6 Mohs for matrix, 7 for quartz; Color: Dark grey to black with white patches; Luster: Dull/earthy matrix, vitreous inclusions; Crystal structure: Aphanitic (fine-grained) matrix; Density: High (2.8–3.0 g/cm3).
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. The white inclusions likely represent secondary mineral growth (vesicle filling) or phenocrysts formed during later stages of cooling.
Uses & applications
Common basalt is used in construction as aggregate for roads, railroad ballast, and in the manufacturing of stone wool insulation. Decorative specimens are used in 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 extremely common on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight for its size, and fine-grained texture that lacks visible individual crystals in the dark matrix. Look for small holes (vesicles) or white mineral spots.
