igneous
Andesite
Andesite (Intermediate Volcanic Rock)
Hardness: 6-7 on Mohs scale. Color: Gray to grayish-green (as seen here). Luster: Dull/earthy (maturation by water wear). Grains: Fine-grained (aphanitic) with small visible phenocrysts of plagioclase.
- Hardness
- 6-7 on Mohs scale
- Color
- Gray to grayish-green (as seen here)
- Luster
- Dull/earthy (maturation by water wear)
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Gray to grayish-green (as seen here). Luster: Dull/earthy (maturation by water wear). Grains: Fine-grained (aphanitic) with small visible phenocrysts of plagioclase.
Formation & geological history
Formed from the cooling of intermediate lava at or near the surface, typically in volcanic arc environments above subduction zones. This specimen shows significant rounding from river or coastal erosion.
Uses & applications
Commonly used as crushed stone for road construction, railroad ballast, and occasionally as decorative stone or landscaping gravel.
Geological facts
Andesite is the second most common volcanic rock in the Earth's crust after basalt. It was named after the Andes Mountains where it is found in abundance.
Field identification & locations
Identify in the field by its characteristic medium-gray color and fine salt-and-pepper texture. Commonly found in mountainous volcanic regions or as rounded pebbles in streambeds near volcanic ranges.
