igneous
Andesite
Intermediate Volcanic Rock (Andesite)
Hardness: 6-7 on Mohs scale. Color: Greenish-grey to dark grey. Luster: Dull/Fine-grained. Crystal Structure: Porphyritic (visible crystals in a fine-grained matrix). Specific Gravity: 2.4-2.8.
- Hardness
- 6-7 on Mohs scale
- Color
- Greenish-grey to dark grey
- Luster
- Dull/Fine-grained
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Greenish-grey to dark grey. Luster: Dull/Fine-grained. Crystal Structure: Porphyritic (visible crystals in a fine-grained matrix). Specific Gravity: 2.4-2.8.
Formation & geological history
Formed through the rapid cooling of intermediate lava at or near the surface, typically in volcanic arcs above subduction zones. This specimen likely dates from the Cenozoic era.
Uses & applications
Commonly used in construction as crushed stone for road beds, aggregate in concrete, and occasionally as pavers or decorative landscape stone.
Geological facts
Andesite is the second most common volcanic rock in Earth's crust after basalt. It is named after the Andes Mountains, where it is found in abundance.
Field identification & locations
Identify in the field by its intermediate color (darker than rhyolite but lighter than basalt) and the presence of small, light-colored plagioclase feldspar phenocrysts. Often found on beaches near volcanic coastlines.
