igneous
Andesite
Intermediate Volcanic Rock (Plagioclase-dominant)
Hardness: 6-7 (Mohs); Color: Grey to dark grey; Luster: Dull/Sub-vitreous; Crystal structure: Aphanitic to porphyritic; Specific gravity: 2.4-2.8
- Hardness
- 6-7 (Mohs)
- Color
- Grey to dark grey
- Luster
- Dull/Sub-vitreous
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Physical properties
Hardness: 6-7 (Mohs); Color: Grey to dark grey; Luster: Dull/Sub-vitreous; Crystal structure: Aphanitic to porphyritic; Specific gravity: 2.4-2.8
Formation & geological history
Formed via the rapid cooling of intermediate-composition lava, typically at convergent plate boundaries and subduction zones. Common in volcanic arc environments.
Uses & applications
Primarily used as crushed stone in construction, road base, and landscape design. Historically used for carving statues and temples in Southeast Asia.
Geological facts
Its name is derived from the Andes Mountains where it is extremely common. It represents the intermediate chemistry between basalt and rhyolite.
Field identification & locations
Identify by its fine-grained grey matrix often containing small visible crystals (phenocrysts). Common in the Pacific Ring of Fire, the Andes, and the Cascades.
