Grey, red, black, altered white/tan, flow-banded pumice dacite

Dacite (pronounced /deɪsaɪt/) is an igneous, volcanic rock with a high iron content. Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere It is intermediate in compositions between andesite and rhyolite, and, like andesite, it consists mostly of plagioclase feldspar with biotite, hornblende, and pyroxene (augite and/or enstatite). For the extinct cephalopod genus see Andesites. Andesite (ˈændəsaɪt is an igneous, Volcanic rock, of intermediate This page is about a volcanic rock For the ghost town see Rhyolite Nevada, and for the satellite system see Rhyolite/Aquacade. Plagioclase is a very important series of tectosilicate Minerals within the Feldspar family Biotite is a common phyllosilicate Mineral within the Mica group with the approximate chemical formula K(Mg Fe3AlSi3O10(F Hornblende is a complex inosilicate 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 The pyroxenes are a group of important rock-forming Silicate minerals found in many Igneous and metamorphic rocks. Augite is a single chain inosilicate Mineral described chemically as (CaMgFeSiO3 or Calcium Magnesium Iron Enstatite is the magnesium endmember of the Pyroxene Silicate mineral series enstatite (MgSiO3 - ferrosilite (FeSiO3 It has an aphanitic to porphyritic texture with quartz as rounded, corroded phenocrysts, or as an element of the ground-mass. Porphyry is a variety of Igneous rock consisting of large-grained Crystals such as Feldspar or Quartz, dispersed in a fine-grained Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in A phenocryst is a relatively large and usually conspicuous Crystal distinctly larger than the grains of the rock groundmass of a Porphyritic Igneous The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram. A QAPF diagram is a double triangle Diagram which is used to classify Igneous rocks based on mineralogic composition Dacite is also defined by silica and alkali contents in the TAS classification. The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide 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 to andesine and labradorite, and is often very zoned. Oligoclase is a rock-forming Mineral belonging to the Plagioclase Feldspars In chemical composition and in its crystallographic and physical characters Andesine is a Feldspar Mineral, a part of the Plagioclase series Labradorite ((CaNa(AlSi4O8 a Feldspar Mineral, is an intermediate to calcic member of the Plagioclase series Sanidine occurs also in some dacites, and when abundant gives rise to rocks that form transitions to the rhyolites. Sanidine is the high temperature form of potassium Feldspar (KNa(SiAl4O8 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; but in many dacites it is largely vitreous, while in others it is felsitic or cryptocrystalline. Tridymite is a high-temperature polymorph of Quartz and usually occurs as minute tabular white or colorless pseudo-hexagonal Triclinic crystals or scales 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 trachytes, and form lava flows, dikes, and in some cases form massive intrusions in the centers of volcanoes. Trachyte is an Igneous, Volcanic rock with an Aphanitic to Porphyritic texture Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures A dike or dyke in Geology is a type of Sheet intrusion referring to any geologic body that cuts Discordantly ' across planar Plate tectonics and hotspots Divergent plate boundaries At the Dacite is an important rock type at Mount St. Helens. Mount St Helens is an active Stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States

The word dacite comes from Dacia, a province of the Roman Empire which lay between the Danube River and Carpathian Mountains (now modern Romania) where the rock was first described. Dacia, in ancient geography was the land of the Dacians. It was named by the ancient Hellenes ( Greeks) " Getae " The Roman Empire was the post-Republican phase of the ancient Roman civilization, characterised by an autocratic form of government and large territorial The Danube (In Donau from earlier Danuvius, Celtic *dānu, meaning "to flow run" Slovak and Polish Dunaj The Carpathian Mountains or Carpathians (Carpaţi Czech, Polish and Slovak: Karpaty; Ukrainian: Карпати Romania ( dated: Rumania, Roumania

This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain. The Encyclopædia Britannica Eleventh Edition (1910–1911 is a 29-volume reference work that marked the beginning of the Encyclopædia Britannica The public domain is a range of abstract materials &ndash commonly referred to as Intellectual property &ndash which are not owned or controlled by anyone