Definition of andesite in US English:



  • A dark, fine-grained, brown or grayish volcanic rock that is intermediate in composition between rhyolite and basalt.

    • ‘The clasts range from angular to subrounded and show a weak preferred orientation when elongate; they include micaceous siltstone, fine-grained sandstone, tuffaceous rock, andesite and medium-grained diorite.’
    • ‘They are marked by eruptions of cooler, stickier lavas such as andesite, dacite and rhyolite.’
    • ‘The main slivers of Devonian rocks found within the fault zone in the Rhynie area are sandstones and andesite in the Rhyme block and the Longcroft Tuffs in the Windyfield block.’
    • ‘Some rocks have basaltic compositions similar to the well-studied meteorites thought to have come from Mars, but other rocks are more like the volcanic rock andesite.’
    • ‘The volcanic strata consist of sheet-like flows of andesite, dacite, basalts, and trachybasalts that are interbedded with agglomerates and tuffs.’


Mid 19th century: named after the Andes mountains, where it is found + -ite.