igneous
Andesite
Andesite (intermediate volcanic rock)
Hardness: 6-7 on Mohs scale; Color: Gray to grayish-green; Luster: Dull or earthy (aphanitic texture); Crystal Structure: Fine-grained matrix with occasional larger phenocrysts; Specific Gravity: 2.4 - 2.8.
- Hardness
- 6-7 on Mohs scale
- Color
- Gray to grayish-green
- Luster
- Dull or earthy (aphanitic texture)
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Gray to grayish-green; Luster: Dull or earthy (aphanitic texture); Crystal Structure: Fine-grained matrix with occasional larger phenocrysts; Specific Gravity: 2.4 - 2.8.
Formation & geological history
Formed through the rapid cooling of intermediate lava at or near the earth's surface, typically at convergent plate boundaries (subduction zones). It consists mainly of plagioclase feldspar, pyroxene, and hornblende.
Uses & applications
Used primarily in the construction industry as crushed stone for road base, aggregate in concrete, and as a fill material. Quality specimens are sometimes used as decorative stone in landscaping.
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 due to the ongoing subduction of the Nazca plate.
Field identification & locations
Identify in the field by its characteristic gray color and fine-grained 'salt and pepper' appearance. It is typically lighter in color than basalt but darker than rhyolite. Found globally in volcanic arcs like the Cascades, the Andes, and Japan.
