igneous
Basalt pebble
Basalt
Hardness: 6.0; Color: Dark grey to greenish-grey; Luster: Dull/Earthy (weathered); Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0
- Hardness
- 6
- Color
- Dark grey to greenish-grey
- Luster
- Dull/Earthy (weathered)
Identified More igneous →
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Physical properties
Hardness: 6.0; Color: Dark grey to greenish-grey; Luster: Dull/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 Earth's surface. This specimen appears water-worn, indicating it was shaped by river or coastal erosion.
Uses & applications
Used extensively in construction as aggregate, for road base, and in railroad ballast. Weathered pebbles like this are common in landscaping and aquarium decor.
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 by its weight (relatively heavy for its size due to iron content), dark color, and lack of visible large crystals. Common in volcanic regions and riverbeds.
