igneous
Andesite
Andesite (contains Plagioclase feldspar, Pyroxene, Hornblende)
Hardness: 6-7 (Mohs); Color: Dark gray to greenish-gray with visible lighter phenocrysts; Luster: Dull/Earthy (matrix) to Vitreous (crystals); Structure: Porphyritic/Aphanitic; Specific Gravity: 2.4-2.8
- Hardness
- 6-7 (Mohs)
- Color
- Dark gray to greenish-gray with visible lighter phenocrysts
- Luster
- Dull/Earthy (matrix) to Vitreous (crystals)
Identified More igneous →
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark gray to greenish-gray with visible lighter phenocrysts; Luster: Dull/Earthy (matrix) to Vitreous (crystals); Structure: Porphyritic/Aphanitic; Specific Gravity: 2.4-2.8
Formation & geological history
Formed through the cooling of intermediate volcanic lava at the Earth's surface, typically at subduction zones above convergent plate boundaries. Most specimens range from Cenozoic to recent times.
Uses & applications
Used primarily in construction for crushed stone, road base, and aggregate. Also used as dimension stone for tiles and landscape decoration.
Geological facts
Andesite is the second most common volcanic rock in the Earth's crust after basalt. It is named after the Andes Mountains, where it is found in great abundance.
Field identification & locations
Identify by its 'salt and pepper' appearance (white plagioclase crystals in a dark matrix) and its intermediate density. Commonly found in volcanic mountain ranges like the Cascades or Andes. Use a hand lens to see small grain textures.
