page_title: Trachyte
section_title: Geographic distribution
hierarchical_section_title: Trachyte / Geographic distribution
caption_attribution_description: English: Photo taken February 20, 1995
context_page_description: Trachyte is an igneous volcanic rock with an aphanitic to porphyritic texture. It is the volcanic equivalent of syenite. The mineral assemblage consists of essential alkali feldspar; relatively minor plagioclase and quartz or a feldspathoid such as nepheline may also be present. Biotite, clinopyroxene and olivine are common accessory minerals.
context_section_description: Trachytes are well represented among the Cenozoic volcanic rocks of Europe. In Britain they occur in Skye as lava flows and as dikes or intrusions, but they are much more common on the continent of Europe, as in the Rhine district and the Eifel, also in Auvergne, Bohemia and the Euganean Hills. In the neighborhood of Rome, Naples and the island of Ischia trachytic lavas and tuffs are of common occurrence. Trachytes are also found on the island of Pantelleria.  In the United States, trachytes crop out extensively in the Davis Mountains, Chisos Mountains, and Big Bend Ranch State Park in the Big Bend (Texas) region, as well as southern Nevada and South Dakota (Black Hills). There is one known voluminous flow from Pu'u Wa'awa'a on the north flank of Hualalai  in Hawaii. In Iceland, the Azores, Tenerife and Ascension there are recent trachytic lavas, and rocks of this kind occur also in New South Wales (Cambewarra Range), Queensland (Main Range), East Africa, Madagascar, Yemen and in many other districts.
  Among the older volcanic rocks trachytes also are not scarce, though they have often been described under the names orthophyre and orthoclase-porphyry, while trachyte was reserved for Tertiary and recent rocks of similar composition. In England there are Permian trachytes in the Exeter district, and Carboniferous trachytes are found in many parts of the central valley of Scotland. The latter differ in no essential respect from their modern representatives in Italy and the Rhine valley, but their augite and biotite are often replaced by chlorite and other secondary products. Permian trachytes occur also in Thuringia and the Saar district in Germany.
  Closely allied to trachyte is the rock type called keratophyre, which is the sodium-rich-plagioclase equivalent of trachyte.
caption: The Breadknife is a peralkaline trachyte dike in the Warrumbungles of eastern Australia
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