igneous
Basalt with Amygdules
Amygdaloidal Basalt
Hardness: 6 (Mohs scale); Color: Dark grey to black matrix with white or green spots; Luster: Dull/earthy matrix with vitreous inclusions; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black matrix with white or green spots
- Luster
- Dull/earthy matrix with vitreous inclusions
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black matrix with white or green spots; Luster: Dull/earthy matrix with vitreous inclusions; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of basaltic lava at the Earth's surface. The white spots (amygdules) are formed when gas bubbles (vesicles) in the cooling lava are later filled with secondary minerals like quartz, calcite, or zeolites.
Uses & applications
Commonly used as crushed stone for road construction, concrete aggregate, and railroad ballast. Exceptionally aesthetic specimens are used in landscaping or kept by hobbyists.
Geological facts
Basalt is the most common rock type on the Earth's crust and also makes up most of the ocean floor. The white patches in this specimen are essentially 'fossilized' gas bubbles from a volcanic eruption that occurred millions of years ago.
Field identification & locations
Identify in the field by its heavy weight, dark color, and characteristic white or light-colored circular mineral infills. It is commonly found in volcanic regions such as the Pacific Northwest, Iceland, or Hawaii.
