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Volcano Calendar 2019
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The Volcano Adventure Guide
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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:
Photos from Kilauea volcano: lava flowing into the sea
Introduction to Plate Tectonics
: The Earth's upper, rigid layer is broken into several plates which are in constant motion to one another. Most earthquakes and volcanoes occur as result of these plate boundaries.
: Watch volcanoes live: our free interactive webcam and online data viewer tool
1-3 day excursions
: If you're interested in volcanoes, there are a number of excursions you should not miss if you're in the area: hike to the craters of Stromboli volcano, climb Etna volcano, get to know the unique volcanic history of Santorini - some examples of shorter (1-3 days) tours and excursions we offer.