igneous
Basalt with Vesicular Amygdule
Extrusive igneous rock (Mafic)
Hardness: 6 on Mohs scale; Color: Dark grey to greenish-grey with lighter mineral infillings; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained) groundmass with mineral crystals filling vesicles; Cleavage: None
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to greenish-grey with lighter mineral infillings
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to greenish-grey with lighter mineral infillings; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained) groundmass with mineral crystals filling vesicles; Cleavage: None
Formation & geological history
Formed from the rapid cooling of magnesium- and iron-rich lava flows at the Earth's surface. Vesicles (gas bubbles) form as volcanic gases escape, which are later filled by secondary minerals like quartz or calcite to form amygdules.
Uses & applications
Used in construction, aggregate, road base, and as decorative stone or collector specimens.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins and forming many volcanic islands like Hawaii and Iceland.
Field identification & locations
Identify in the field by its dark, fine-grained matrix, often containing visible cavities or filled pockets (amygdules). Found globally in volcanic regions.
