Igneous
Basalt (Water-worn Pebble)
Basalt (Mafic volcanic rock)
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Matte (when unpolished), Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific gravity: 2.8–3.0
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Matte (when unpolished), Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specific specimen has been Rounded by fluvial or marine erosion (water action).
Uses & applications
Used extensively in construction (aggregate, road base), industrial applications (stone wool insulation), and occasionally in jewelry as 'river stone' beads or for lithotherapy/massage stones.
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 in the field by its dark color, heavy weight for its size, and the absence of visible large crystals. Commonly found along coastlines, riverbeds, and volcanic fields.
