What type of magma is dacite?
Dacite lavas are viscous and tend to form thick blocky lava flows or steep-sided piles of lava called lava domes. Dacitic magmas tend to erupt explosively, thus also ejecting abundant ash and pumice.
What is dacite rock made of?
Like andesite, dacite consists mostly of plagioclase feldspar with biotite, hornblende, augite, or enstatite and generally has a porphyritic structure (scattered larger crystals in a fine-grained groundmass); additionally, however, it contains quartz as rounded, corroded crystals or grains, or as a constituent of the …
How is a porphyritic rock formed?
A porphyritic texture is developed when magma that has been slowly cooling and crystallising within the Earth’s crust is suddenly erupted at the surface, causing the remaining uncrystallised magma to cool rapidly. This texture is characteristic of most volcanic rocks. This texture is exhibited by some volcanic rocks.
What type of igneous rock is dacite?
Dacite is a felsic extrusive rock, intermediate in composition between andesite and rhyolite. It is often found associated with andesite, and forms lava flows, dikes, and, in some cases, massive intrusions in the centres of old volcanoes. Dacite is the volcanic equivalent of granodiorite.
What rock is formed from magma?
igneous rock
Extrusive, or volcanic, igneous rock is produced when magma exits and cools above (or very near) the Earth’s surface. These are the rocks that form at erupting volcanoes and oozing fissures.
How is basalt formed?
Basalts are formed by the rapid cooling of basaltic lava, equivalent to gabbro-norite magma, from interior of the crust and exposed at or very close to the surface of Earth. These basalt flows are quite thick and extensive, in which gas cavities are almost absent.
Is dacite an igneous rock?
Dacite is a fine-grained igneous rock that is normally light in color. It is often porphyritic. Dacite is found in lava flows, lava domes, dikes, sills, and pyroclastic debris. It is a rock type usually found on continental crust above subduction zones, where a relatively young oceanic plate has melted below.
Where do you find dacite?
Dacite is found in lava flows, lava domes, dikes, sills, and pyroclastic debris. It is a rock type usually found on continental crust above subduction zones, where a relatively young oceanic plate has melted below.
How is dacite rock formed?
Dacite (/ˈdeɪsaɪt/) is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite.
Where are porphyritic rocks found?
Porphyritic textures are most common in volcanic rocks where one of the minerals will begin to crystallize prior to eruption (therefore producing larger grains), with the rest cooling more rapidly after eruption.
How do you identify porphyritic rocks?
Porphyritic intrusive rocks have a matrix with individual crystals easily distinguished with the eye, but one group of crystals appearing clearly much bigger than the rest, as in a porphyritic granite. The term comes from the Ancient Greek πορφύρα (porphyra), meaning “purple”.