What Is Trachyte?

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  • Written By: Glyn Sinclair
  • Edited By: Rachel Catherine Allen
  • Last Modified Date: 04 November 2018
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Trachyte is an extrusive igneous volcanic rock. Extrusive refers to the ejection of the rock from the earth during an eruption of magma, and igneous refers to the rock having solidified and later cooled from lava. Its texture can be finely grained or rough. The trachyte is primarily composed of minerals that are rich in alkali elements. Sometimes the cooling is so quick that tiny beads of glass actually form within the trachyte.

These volcanic rocks are made up primarily of sanidine feldspar. Feldspar refers to groupings of minerals that consist of aluminum, potassium, sodium and calcium and these minerals that make up almost all crystalline rocks. These rocks typically have very small steam cavities that tend to make the surface irregular. Trachyte can often have bands or streaks running through it due to flow lines of congealed lava. Although rare, quartz may also be present in the rock.

Trachyte rocks are generally deemed to be porphyritic in nature. This means that they can be studded with sizeable crystals in an otherwise finely textured mass. They are found in significant numbers during the tertiary period. This geological term refers to the period dating back from 2.6 million years to 65 million years. Trachytes are commonly found in Europe and especially in Germany’s Rhine district.


These volcanic rocks are sometimes rich in silica and have been used by humans since Roman times. They range in color from violet to pink to grey and were used for paving streets as well as sculptures, and even constructing furniture. Venice’s St. Mark square is actually paved with trachyte. Mt Kilimanjaro in Africa, as well as Mt Erebus in Antarctica, are both examples of trachyte volcanoes. Trachyte is thought to be the volcanic equivalent of svenite, which is a rock that has been forced by magma into the cracks of other rocks and crystallized, yet not quite reaching the earth’s surface.

Volcanology deals with the study of volcanoes and lava as well as geochemical and geological occurrences. This field of study is thousands of years old and rock paintings of erupting volcanoes date back to the Neolithic period in Turkey. Volcanologists employ seismographs to detect increased activity in and around active volcanoes. After a volcano has erupted, geological experts will often study rocks such as trachytes from the magma ejection to gain a better knowledge of the earth’s crust and its movements. The word volcanology is taken from the Latin word Vulcan, who was considered the Roman god of fire.


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