igneous
Basalt with Amygdule
Aphanitic Mafic Volcanic Rock (Basalt) with Zeolite/Quartz Infill
Hardness: 5-6 (matrix); Color: Dark grey to black matrix with white/pink mineral inclusion; Luster: Dull/earthy matrix, vitreous inclusion; Texture: Fine-grained (aphanitic)
- Hardness
- 5-6 (matrix)
- Color
- Dark grey to black matrix with white/pink mineral inclusion
- Luster
- Dull/earthy matrix, vitreous inclusion
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Physical properties
Hardness: 5-6 (matrix); Color: Dark grey to black matrix with white/pink mineral inclusion; Luster: Dull/earthy matrix, vitreous inclusion; Texture: Fine-grained (aphanitic)
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. The white spot is an amygdule, formed when gas bubbles (vesicles) in the cooling lava were later filled with secondary minerals like quartz, calcite, or zeolites through hydrothermal activity.
Uses & applications
Basalt is primarily used as an aggregate in construction (roads, concrete). Specimen pieces with mineral inclusions are used for geological study and mineral collecting.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Large-scale basalt formations are called 'traps' or 'flood basalts'.
Field identification & locations
Identified in the field by its dark color, heavy weight (relative to size), and fine-grained texture. Amygdaloidal varieties are common in volcanic regions like the Pacific Northwest or the Lake Superior region.
