igneous
Basalt River Pebble
Basalt (Extrusive Igneous Rock)
Hardness: 5-6 (Mohs); Color: Dark grey to black or brownish-black; Luster: Dull to earthy (weathered); Crystal structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to black or brownish-black
- Luster
- Dull to earthy (weathered)
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to black or brownish-black; Luster: Dull to earthy (weathered); 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 surface of a terrestrial planet or the moon. This specific item is a water-worn pebble, likely shaped by river or coastal erosion over centuries.
Uses & applications
Commonly used in construction as aggregate, in road base, and for river stone landscaping. Small smooth pebbles like this are popular for massage stones (hot stone therapy) and decorative garden features.
Geological facts
Basalt is the most common rock type in Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars. Darker basalt often contains small amounts of olivine or pyroxene.
Field identification & locations
Identified in the field by its dark color, heavy weight (relative to size), and lack of visible crystals to the naked eye. This specimen's rounded shape indicates it has been tumbled by water flow. Common in volcanic regions or riverbeds.
