igneous
Andesite
Intermediate Volcanic Rock (Andesite)
Hardness: 6-7 (Mohs scale), Color: light to dark gray/greenish-gray, Luster: dull or sub-vitreous, Crystal Structure: fine-grained (aphanitic) often with larger phenocrysts (porphyritic), Specific Gravity: 2.4-2.8
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Physical properties
Hardness: 6-7 (Mohs scale), Color: light to dark gray/greenish-gray, Luster: dull or sub-vitreous, Crystal Structure: fine-grained (aphanitic) often with larger phenocrysts (porphyritic), Specific Gravity: 2.4-2.8
Formation & geological history
Formed through the cooling of intermediate lava at volcanic arcs above subduction zones; primarily composed of plagioclase feldspar and pyroxene or hornblende.
Uses & applications
Used extensively in the construction industry as crushed stone for road base, concrete aggregate, and railroad ballast; occasionally used for tiles or decorative monuments.
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 abundance.
Field identification & locations
Identify in the field by its intermediate gray color and typical occurrence in volcanic terrains; look for small visible crystals of feldspar or darker minerals embedded in a fine-grained matrix.
