igneous
Basalt with Secondary Mineral Inclusions
Amygdaloidal Basalt (Mafic volcanic rock, primarily Augite and Plagioclase)
Hardness: 6.0-7.0 (Mohs); Color: Dark grey to charcoal with reddish oxide staining; Luster: Dull, earthy matrix with vitreous inclusions; Structure: Fine-grained aphanitic matrix; Specific Gravity: 2.8-3.0.
- Hardness
- 6
- Color
- Dark grey to charcoal with reddish oxide staining
- Luster
- Dull, earthy matrix with vitreous inclusions
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Physical properties
Hardness: 6.0-7.0 (Mohs); Color: Dark grey to charcoal with reddish oxide staining; Luster: Dull, earthy matrix with vitreous inclusions; Structure: Fine-grained aphanitic matrix; Specific Gravity: 2.8-3.0.
Formation & geological history
Formed through the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The vesicular or 'pitted' texture suggests gas bubbles were trapped during cooling, later potentially filled by secondary minerals (amygdules) like quartz or calcite.
Uses & applications
Common basalt is used extensively in construction as aggregate for roads and railways, and in high-strength concrete. Rare or mineral-rich specimens are kept for geological study and private collections.
Geological facts
Basalt is the most common rock type on the Earth's surface and makes up most of the ocean floor. It is also prevalent on Mars and the Moon.
Field identification & locations
Identify by its heavy weight (high density), dark color, and fine crystalline grain. Commonly found in volcanic regions such as the Pacific Northwest, Iceland, and Hawaii. Look for 'vuggy' or holey textures that indicate volcanic gas escape.
