What is trachyte rock?
trachyte, light-coloured, very fine-grained extrusive igneous rock that is composed chiefly of alkali feldspar with minor amounts of dark-coloured minerals such as biotite, amphibole, or pyroxene. Compositionally, trachyte is the volcanic equivalent of the plutonic (intrusive) rock syenite.
Is trachyte porphyry intrusive or extrusive?
extrusive rock
Trachyte is an extrusive rock, belonging to the alkali series of intermediate volcanic rocks.
Is andesite a porphyritic?
Andesite most commonly denotes fine-grained, usually porphyritic rocks; in composition these correspond roughly to the intrusive igneous rock diorite and consist essentially of andesine (a plagioclase feldspar) and one or more ferromagnesian minerals, such as pyroxene or biotite.
How is trachyte porphyry formed?
Trachyte is associated with other lavas in volcanic regions and it have been formed by the crystallization and abstraction of iron, magnesium, and calcium minerals from a parent basaltic lava. Group: volcanic. Colour: variable but often light coloured, generally light coloured phenocrysts.
How is porphyry rock formed?
Porphyritic rocks are a product of igneous differentiation, and are generally formed when a column of rising magma is cooled in two stages: In the first stage, the magma is cooled slowly deep in the crust, creating the large crystal grains, with a diameter of 2mm or more.
Is andesite intrusive or extrusive?
extrusive igneous rock
Porphyritic texture — andesite: This is an extrusive igneous rock. The magma from which it formed cooled slowly for a while deep below the surface (forming the large crystals), then finished cooling very quickly when it was ejected at the surface, forming the fine-grained groundmass.
What is andesite porphyry?
Andesite-porphyry is a porphyry with andesitic chemism. The term “porphyry” is used for igneous rock composed of large, conspicuous crystals (phenocrysts) and a fine grained to glassy groundmass (matrix) in which the phenocrysts are embedded.
How is andesite porphyry formed?
Andesite Porphyry When the magma erupts onto the Earth’s surface, the rest of the melt crystallizes quickly. This produces a rock with two different crystal sizes: large crystals that formed slowly at depth (the “phenocrysts”), and small crystals that formed quickly at the surface (known as “groundmass”).
How is a trachyte formed?
Trachyte (/ˈtreɪkaɪt, ˈtrækaɪt/) is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava enriched with silica and alkali metals. It is the volcanic equivalent of syenite.
What is rock porphyry?
(A porphyry is an igneous rock containing conspicuous crystals, called phenocrysts, surrounded by a matrix of finer-grained minerals or glass or both.) In most rocks, both alkali and plagioclase feldspars occur as irregularly shaped grains with only a few or no crystal faces.
What is the difference between porphyry and andesite?
Andesite is a dark, fine-grained, brown or greyish intermediate volcanic rock which is a commonly found in lava. Porphyry is a reddish-brown to purple igneous rock containing large phenocrysts of various minerals embedded in a fine-grained matrix. These rocks are composed of many distinct minerals.
What is trachyte porphyry?
Trachyte Porphyry. An igneous rock, trachyte primarily consists of alkali feldspars, but also contains plagioclase as well as minor amounts of other minerals, such as olivine, biotite, and pyroxene. It is commonly considered to form via the crystallization and extraction of magnesium, iron, and calcium from a basaltic magma.
What is the difference between trachyte and trachydacite?
Trachydacite occupies the same field in the TAS diagram as trachyte, but is distinguished from trachyte by a normative quartz content over 20%. Trachydacite is not a recognized rock type in the QAPF classification, where rocks rich in alkali feldspar and with quartz over 20% would be classified as rhyolites.
What type of igneous rock is trachyte?
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.