Main Page | See live article | Alphabetical index Trachyte is an igneous, volcanic (extrusive) rock, with aphanitic to porphyritic texture. Mineral assembly is usually, alkali feldspar and plagioclase (in a ratio > 1:4). Quartz is absent. Biotite, pyroxene and scarce olivine are common accessory minerals. See also: igneous rocks, list of rocks This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.