igneous
Basalt Pebble with Quartz Inclusion
Basalt (SiO2 with Fe, Mg silicates) with Quartz (SiO2)
Hardness: 6-7 on Mohs scale. Color: Dark gray to black main body with a small tan/white quartz or chalcedony pocket. Luster: Dull to earthy for the basalt matrix, vitreous for the inclusion. Cleavage: None. Texture: Very fine-grained (aphanitic), rounded and smoothed by water erosion.
- Hardness
- 6-7 on Mohs scale
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Dark gray to black main body with a small tan/white quartz or chalcedony pocket. Luster: Dull to earthy for the basalt matrix, vitreous for the inclusion. Cleavage: None. Texture: Very fine-grained (aphanitic), rounded and smoothed by water erosion.
Formation & geological history
Formed from the rapid cooling of basaltic lava at or near the Earth's surface, followed by secondary mineral deposition (quartz/calcite) in a small vesicle or cavity. Later eroded and rounded by river or beach wave action.
Uses & applications
Commonly found in natural collections; basalt is widely used in construction, road aggregates, and landscaping, while river pebbles are used in decorative garden features and aquariums.
Geological facts
Basalt is the most common rock type in the Earth's crust, forming almost all oceanic crust as well as major flood basalt plateaus. Small nodules or amygdules often form inside ancient gas bubbles within the lava.
Field identification & locations
Identified by its fine-grained dark matrix and water-worn, smooth pebble shape featuring a small lighter-colored mineral inclusion. Commonly found along stream beds, riverbanks, and oceanic coastlines.
