Igneous
Basalt River Pebble
Extrusive mafic igneous rock; primarily composed of Plagioclase Feldspar and Pyroxene
Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull to waxy when polished; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0; No visible cleavage in hand specimen.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to waxy when polished
Identified More igneous →
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull to waxy when polished; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0; No visible cleavage in hand specimen.
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 fluvial (river) or marine erosion over hundreds to thousands of years.
Uses & applications
Commonly used in landscaping, as decorative 'river stones,' in construction aggregate, and frequently in hot stone massage due to its high heat retention properties.
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.
Field identification & locations
Identify in the field by its dark color, heavy weight for its size, and the lack of visible crystals. Commonly found in riverbeds, beaches, and volcanic fields worldwide. Collectors should look for unique shapes or vesicles (gas bubbles).
