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Illustrated Volcano Glossary
Dacite is an igneous, volcanic rock with a high iron content found at many lava-domes.
Dacite (pronounced /deɪsaɪt/) is an igneous, volcanic rock with a high iron content. 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). It has an aphanitic to porphyritic texture with quartz as rounded, corroded phenocrysts, 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. Dacite is also defined by silica and alkali contents in the TAS classification.
The plagioclase ranges from oligoclase to andesine and labradorite, and is often very zoned. Sanidine 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; 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.
The rocks of this group occur in Romania, Almeria (Spain), Argyll and other parts of Scotland, Bardon Hill in Leicestershire, New Zealand, the Andes, Martinique, Nevada and other regions of western North America, Greece (Methana, Nisyros, Santorini) as well as other places. They are mostly associated with andesites and trachytes, and form lava flows, dikes, and in some cases form massive intrusions in the centers of volcanoes. Dacite is an important rock type at Mount St. Helens.
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.
More on VolcanoDiscovery:
Volcano Special Tours
: We organize tours to particularly active volcanoes and during ongoing eruptions for extended observation time from various viewpoints. These trips, exclusively for very small groups, are often announced only at short notice and require fast travel and flexibility. Each trip is accompanied by a volcanologist from our team. Examples include: Kilauea (Hawai'i), Colima (Mexico), Krakatau and many others.
Dukono volcano photos
: Dukono on Halmahera in Indonesia has been in permanent activity for years, often producing ash plumes that drift around the northern part of the island and have become normality.
Nyamuragira volcano photos
: Africa's version of Mauna Loa, Nyamuragira (or Nyamulagira) is a massive basaltic shield volcano neighboring Nyiragongo. It is one of the most active volcanoes in the world and has voluminous eruptions every few years.
Latest VAAC alerts
: The Volcanic Ash Advisory Centers provide near-real time global monitoring of volcanic ash plumes for aviation. Read the latest (or browse past) advisories.