Andesite
Image: Smithsonian Institution (CC0)
Mineral NameAndesite
Chemical FormulaIntermediate silicate rock, rich in plagioclase feldspar
Mohs Hardness6
Crystal Systemamorphous
Lusterdull
Streak Colorgrayish-white
Cleavageabsent
Fractureuneven
Specific Gravity2.65
Colorsdark gray, black
Transparencyopaque
Type LocalityParícutin volcano, Michoacán, Mexico
Mineral GroupSilicates
Usesconstruction aggregate, road building, landscaping
Associated Mineralsplagioclase feldspar, pyroxene, amphibole, biotite
Raritycommon
Description
A dark gray to black, vesicular volcanic rock with a fine-grained texture, showing some lighter specks which could be phenocrysts or vesicle infillings.
Geological Context
Andesite forms from the rapid cooling of intermediate lava flows, typically found in volcanic arcs above subduction zones, such as the Pacific Ring of Fire.
