igneous
Basalt Pebble
Basalt
AI-generated identification · may be incorrectHardness: 6 on the Mohs scale. Color: Dark gray to black, often with a fine-grained, aphanitic matrix and occasional small light or dark phenocrysts. Luster: Dull to sub-vitreous. Specific Gravity: 2.8 - 3.0. Crystal Structure: Fine-grained/aphanitic (microcrystalline silicate matrix).
- Hardness
- 6 on the Mohs scale
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on the Mohs scale. Color: Dark gray to black, often with a fine-grained, aphanitic matrix and occasional small light or dark phenocrysts. Luster: Dull to sub-vitreous. Specific Gravity: 2.8 - 3.0. Crystal Structure: Fine-grained/aphanitic (microcrystalline silicate matrix).
Formation & geological history
Formed from the rapid cooling of mafic lava rich in iron and magnesium at or near the Earth's surface, typically at mid-ocean ridges, volcanic island arcs, and continental flood basalt provinces.
Uses & applications
Commonly used as crushed stone in construction, road base, asphalt concrete, railroad ballast, and decorative landscaping pebbles.
Geological facts
Basalt is the most common rock type in the Earth's crust, forming the vast majority of oceanic crust, as well as large regions of the Moon (the dark lunar maria).
Field identification & locations
Identify in the field by its dense, heavy feel, fine-grained dark gray or black color, and lack of visible quartz crystals. Extensively found along volcanic coasts, riverbeds near volcanic areas, and glacial gravel deposits.
