igneous
Basalt (Beach Pebble)
Extrusive mafic volcanic rock
Hardness: 6.0; Color: Dark grey to black with possible green/blue tint; Luster: Dull or waxy when wet; Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0
- Hardness
- 6
- Color
- Dark grey to black with possible green/blue tint
- Luster
- Dull or waxy when wet
Identified More igneous →
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Physical properties
Hardness: 6.0; Color: Dark grey to black with possible green/blue tint; Luster: Dull or waxy when wet; 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 very near the Earth's surface. This specimen has been rounded and smoothed by water erosion through river or coastal wave action.
Uses & applications
Crushed stone for road base, concrete aggregate, railroad ballast, and sometimes used for stone massage or aquarium decoration.
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 heavy weight (density), dark color, and fine grain where crystals are not visible to the naked eye. Often shows small pits or 'vesicles' if it cooled with gas bubbles.
