igneous
Basalt (River Pebble)
Extrusive mafic igneous rock
Hardness: 6-7 Mohs; Color: dark grey to black with brown weathering; Lustre: dull/earthy; Crystal structure: aphanitic (fine-grained); Specific gravity: 2.8-3.0.
- Hardness
- 6-7 Mohs
- Color
- dark grey to black with brown weathering
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: dark grey to black with brown weathering; Lustre: dull/earthy; Crystal structure: aphanitic (fine-grained); 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. This specific specimen has been rounded and smoothed by water transport in a river or coastal environment.
Uses & applications
Commonly used as aggregate in construction, road base, and landscaping. Small pebbles are often used in decorative gardening or as pocket stones.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It also exists on the Moon and Mars.
Field identification & locations
Identify by its heavy weight relative to its size, dark interior color, and fine-grained texture lacking visible crystals. Often found in riverbeds or near volcanic regions.
