Dacite

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Dacite

Dacite is an igneous

Igneous rock

Igneous rock is one of the three main Rock types . Igneous rock is formed by magma being cooled and becoming solid . They may form with or without crystallization, either below the surface as Intrusion rocks or on the surface as extrusive rocks....
, volcanic rock

Volcanic rock

Volcanic rock is an igneous rock of Volcano origin.Texture Volcanic rocks are usually fine-grained or aphanitic to glassy in texture....
with a high iron content. It is intermediate in compositions between andesite

Andesite

Andesite is an igneous rock, volcanic rock, of Igneous rock#Chemical classification, with aphanitic to porphyritic texture. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende....
and rhyolite

Rhyolite

This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous rock, volcanic rock , of felsic composition ....
, and, like andesite, it consists mostly of plagioclase

Plagioclase

Plagioclase is a very important series of Silicate minerals minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series ....
feldspar with biotite

Biotite

Biotite is a common Silicate minerals#Phyllosilicates mineral within the mica group, with the approximate chemical formula K3AlSi3O102....
, hornblende

Hornblende

Hornblende is a complex silicate minerals series of minerals. Hornblende is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole....
, and pyroxene

Pyroxene

The pyroxenes are a group of important rock-forming silicate minerals found in many igneous and metamorphic rock rock . They share a common structure comprised of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems....
(augite

Augite

Augite is a Silicate_minerals#Single_chain_inosilicates: mineral described chemically as SiO3 or calcium magnesium iron silicate. The crystals are monoclinic and prismatic....
and/or enstatite

Enstatite

Enstatite is the magnesium endmember of the pyroxene silicate mineral series enstatite - ferrosilite . The magnesium rich members of the solid solution series are common rock-forming minerals found in igneous and metamorphic rock rocks....
). It has an aphanitic to porphyritic texture with quartz

Quartz

Quartz is the most abundant mineral in the Earth's continental crust . It is made up of a Crystal structure of silica tetrahedra. Quartz has a hardness of 7 on the Mohs scale and a density of 2.65 g/cm?....
as rounded, corroded phenocryst

Phenocryst

A phenocryst is a relatively large and usually conspicuous crystal distinctly larger than the grains of the rock Matrix of a porphyritic igneous rock....
s, or as an element of the ground-mass.

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Encyclopedia

Dacite is an igneous

Igneous rock

Volcanic rock

Andesite

Rhyolite

Plagioclase

Biotite

Biotite is a common Silicate minerals#Phyllosilicates mineral within the mica group, with the approximate chemical formula K3AlSi3O102....
, hornblende

Hornblende

Pyroxene

Augite

Augite is a Silicate_minerals#Single_chain_inosilicates: mineral described chemically as SiO3 or calcium magnesium iron silicate. The crystals are monoclinic and prismatic....
and/or enstatite

Enstatite

Quartz

Phenocryst

A phenocryst is a relatively large and usually conspicuous crystal distinctly larger than the grains of the rock Matrix of a porphyritic igneous rock....
s, or as an element of the ground-mass. The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram

QAPF diagram

A QAPF diagram is a double triangle diagram which is used to classify igneous rocks based on mineralogy composition. The acronym, QAPF, stands for "Quartz, feldspar, Plagioclase, Feldspathoid "....
. Dacite is also defined by silica and alkali contents in the TAS classification

TAS classification

The TAS classification can be used to assign names to many common types of volcanic rocks based upon the relationships between the combined alkali content and the silica content....
.

The plagioclase ranges from oligoclase

Oligoclase

Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. In chemical composition and in its crystallographic and physical characters it is intermediate between albite and anorthite ....
to andesine

Andesine

Andesine is a feldspar mineral, a part of the plagioclase series.File:01722 Andesine.jpgIt is usually defined as having "%An" between 30 and 50....
and labradorite

Labradorite

Labradorite , a feldspar mineral, is an intermediate to calcic member of the plagioclase series. It is usually defined as having "%An" between 50 and 70....
, and is often very zoned. Sanidine

Sanidine

Sanidine is the high temperature form of potassium feldspar 4O8. Sanidine most typically occurs in felsic volcanic rocks such as obsidian, rhyolite and trachyte....
occurs also in some dacites, and when abundant gives rise to rocks that form transitions to the rhyolites. The biotite is brown; the hornblende brown or greenish brown; and the augite is usually green.

The groundmass of these rocks is often microcrystalline, with a web of minute feldspars mixed with interstitial grains of quartz or tridymite

Tridymite

Tridymite is a high-temperature polymorphism of quartz and usually occurs as minute tabular white or colorless pseudo-hexagonal triclinic crystals, or scales, in cavities in acidic volcanic rocks....
; but in many dacites it is largely vitreous, while in others it is felsitic or cryptocrystalline. In hand specimen many of the hornblende and biotite dacites are grey or pale brown and yellow rocks with white feldspars, and black crystals of biotite and hornblende. Other dacites, especially augite and enstatite dacites, are darker colored.

Dacites are mostly associated with andesites and trachyte

Trachyte

Trachyte is an igneous, volcanic rock with an aphanitic to porphyritic texture. The mineral assemblage consists of essential alkali feldspar; relatively minor plagioclase and quartz or a feldspathoid such as nepheline may also be present....
s, and form lava flows, dike

Dike (geology)

A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...
s, and in some cases form massive intrusions in the centers of volcano

Volcano

A volcano is an opening, or rupture, in a planet's surface or Crust , which allows hot, molten rock, ash, and gases to escape from below the surface....
es.

The word dacite comes from Dacia

Dacia

In ancient geography, Dacia was the land of the Dacians. It was named by the ancient Greeks "Getae". Dacia was a large district of East-Central Europe, bounded on the north by the Carpathian Mountains, on the south by the Danube, on the west by the Tisia or Tisza, on the east by the Tyras or Dniester, now in eastern Moldova....
, a province of the Roman Empire

Roman Empire

The Roman Empire was the Roman Republic phase of the Ancient Rome, characterised by an autocracy form of government and large territorial holdings in Europe and around the Mediterranean....
which lay between the Danube River and Carpathian Mountains

Carpathian Mountains

The Carpathian Mountains or Carpathians are a range of mountains forming an arc of roughly 1,500 km across Central Europe and Eastern Europe, making them the largest mountain range in Europe....
(now modern Romania

Romania

Romania is a country located in Southeastern Europe Central Europe, North of the Balkan Peninsula, on the Lower Danube, within and outside the Carpathian Mountains, bordering on the Black Sea....
) where the rock was first described.