igneous
Basalt (River Pebble)
Mafic volcanic rock (primarily Plagioclase feldspar and Pyroxene)
Hardness: 6 (Mohs scale). Color: Dark grey to charcoal black. Luster: Dull/Earthy. Structure: Aphanitic (fine-grained), rounded by water erosion. Specific Gravity: 2.8–3.0.
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to charcoal black
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6 (Mohs scale). Color: Dark grey to charcoal black. Luster: Dull/Earthy. Structure: Aphanitic (fine-grained), rounded by water erosion. 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 further shaped by fluvial (river) or coastal erosion, smoothing its edges over thousands of years.
Uses & applications
Used extensively in construction as aggregate (crushed stone), for paving (cobblestones), and as thermal mass in saunas. In natural pebble form, it is used for decorative landscaping and massage therapy 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, Mars, and Venus in the form of 'maria' or vast plains.
Field identification & locations
Identify by its heavy weight relative to size (high density), dark matte color, and lack of visible crystals to the naked eye. Commonly found in volcanic regions, riverbeds, and coastal beaches.
