igneous
Basalt (Vesicular and Scoria)
Basalt (extrusive volcanic rock)
Hardness: 6-7 (Mohs); Color: Dark grey, black, or reddish-brown; Luster: Dull to sub-metallic; Structure: Aphanitic to vesicular (porous); Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 (Mohs)
- Color
- Dark grey, black, or reddish-brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark grey, black, or reddish-brown; Luster: Dull to sub-metallic; Structure: Aphanitic to vesicular (porous); Specific Gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the Earth's surface. These specimens exhibit a vesicular texture, meaning gas bubbles were trapped as the lava solidified.
Uses & applications
Used extensively in construction as aggregate, road base, railroad ballast, and in the production of stone wool insulation. High-porosity varieties (lava rock) are used in landscaping and gas grills.
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 in abundance on the Moon and Mars.
Field identification & locations
Identify in the field by its heavy weight (relative to size), dark color, and presence of small holes or 'vesicles.' Commonly found in volcanic fields, oceanic islands (like Hawaii), and mid-ocean ridges.
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