page_title: Dacite
section_title: Texture
hierarchical_section_title: Dacite / Texture
caption_attribution_description: English: Photograph by Daniel Mayer. Taken in October 2003
context_page_description: Dacite is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. The word dacite comes from Dacia, a province of the Roman Empire which lay between the Danube River and Carpathian Mountains where the rock was first described.
  The term dacite was introduced in the scientific literature by the Austrian geologist Guido Stache, and used for the first time in the book Geologie Siebenbürgens. The reason to designate a new igneous rock type was to discriminate between the oligoclase-bearing rocks and the orthoclase-bearing rocks on petrographic grounds.
  The type-locality of dacite is near the village of Poieni, Cluj located along the Crișul Repede river, Vlădeasa Massif in the northern Apuseni Mountains, Romania.
context_section_description: 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 pyroxene-bearing dacites, are darker colored.
  In thin section, dacites may have an aphanitic to porphyritic texture. Porphyritic dacites contain blocky highly zoned plagioclase phenocrysts and/or rounded corroded quartz phenocrysts. Subhedral hornblende and elongated biotite grains are present. Sanidine phenocrysts and augite (or enstatite) are found in some samples. The groundmass of these rocks is often aphanitic 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.
caption: Grey, red, black, altered white/tan, flow-banded pumice dacite
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