What is dacite?
What Is Dacite? 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.
What minerals are found in dacite?
Other minerals that might be found in dacite include quartz, biotite, hornblende, augite, and enstatite. Dacites consisting mostly of plagioclase and quartz are usually light in color, often white to light gray. Those with abundant hornblende and biotite can be light gray to light brown.
What is the role of dacite in the formation of crust?
Dacite's role in the creation of Archean continental crust. The process by which dacite forms has been used to explain the generation of continental crust during the Archean eon. At that time, the fabrication of dacitic magma was more ubiquitous due to the availability of young hot oceanic crust.
What is a dacite projectile point?
Dacite Projectile Point: Fine-grained dacite with a uniform texture can be knapped into small tools and weapons. This Native American projectile point was knapped from black dacite. Found in southeastern Montana. Approximately 7/8 inch long and 1/2 inch wide.
What is equivalent of dacite?
Dacite is the volcanic equivalent of granodiorite.
What is dacite rock?
dacite, volcanic rock that may be considered a quartz-bearing variety of andesite. Dacite is primarily associated with andesite and trachyte and forms lava flows, dikes, and sometimes massive intrusions in the centres of old volcanoes.
What is rhyolite used for?
Rhyolite is suitable as aggregate, fill-in construction, building material and road industries, decorative rock in landscaping, cutting tool, abrasive and jewelry. FIGURE 4.33.
How is dacite 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.
Is dacite a mineral?
Dacite can be considered the fine-grained equivalent of granodiorite. Plagioclase is the most abundant mineral in many dacites. Other minerals that might be found in dacite include quartz, biotite, hornblende, augite, and enstatite.
Can dacite be red?
Red dacite can be found in Lassen Volcanic at several sites; for example, in the Chaos Crater area at the end of Chaos Crags Trail. Also, along the Devasteted Area Trail you can touch a giant boulder of red dacit at the “Old Giants” interpretive exhibit.
Is gold found in rhyolite?
Published research on the Sleeper Rhyolite has indicated that these rocks represent an ancient epithermal gold deposit (hot springs gold deposit), formed by volcanism during extensional Basin & Range tectonics.
Where is rhyolite most commonly found?
Rhyolite has the mineralogical composition of granite. Rhyolite rocks can be found in many countries including New Zealand, Germany, Iceland, India, and China, and the deposits can be found near active or extinct volcanoes.
What gems are found in rhyolite?
Rhyolite and Gemstones Topaz, agate, jasper, red beryl, and opal are a few of the crystals and gems that occur in rhyolite.
What is dacite magma?
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.
Is dacite volcanic or plutonic?
Main types of igneous rocksWeight % of SiO2Plutonic rock typeVolcanic rock equivalent45-53GabbroBasalt53-63DioriteAndesite63-68GranodioriteDacite68-75GraniteRhyolite
Is dacite an extrusive igneous rock?
Dacite is an extrusive igneous rock. The principle minerals that make up dacite are plagioclase, quartz, pyroxene, or hornblende.
Overview
Dacite 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. It is composed predominantly of plagioclase feldspar and quartz.
Dacite is relatively common, occurring in many tectonic settings. It is associat…
Composition
Dacite consists mostly of plagioclase feldspar and quartz with biotite, hornblende, and pyroxene (augite or enstatite). The quartz appears as rounded, corroded phenocrysts, or as an element of the ground-mass. The plagioclase in dacite ranges from oligoclase to andesine and labradorite. Sanidine occurs, although in small proportions, in some dacites, and when abundant gives rise to rocks tha…
Texture
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 …
Geological context and formation
Dacite usually forms as an intrusive rock such as a dike or sill. Examples of this type of dacite outcrop are found in northwestern Montana and northeastern Bulgaria. Nevertheless, because of the moderately high silica content, dacitic magma is quite viscous and therefore prone to explosive eruption. A notorious example of this is Mount St. Helens in which dacite domes formed from previo…
Distribution
Dacite is relatively common and occurs in various tectonic and magmatic contexts:
• In oceanic volcanic series. Examples: Iceland (Heiðarsporður ridge), Juan de Fuca Ridge
• In calc-alkaline and tholeiitic volcanic series of the subduction zones of island arcs and active continental margins. Examples of dacitic magmatism in island arcs are Japan, the Philippines, the Aleutians, the Antilles, the Sunda Arc (Mount Batur), Tonga and the South Sandwich Islands. Examples of da…
Etymology
The word dacite comes from Dacia, a province of the Roman Empire which lay between the Danube River and Carpathian Mountains (now modern Romania and Moldova) where the rock was first described.
The term dacite was used for the first time in the scientific literature in the book "Geologie Siebenbürgens" ("The Geology of Transylvania") by Austrian geologists Franz Ritter von Hauer an…
See also
• Lassen Volcanic National Park – National park in California, United States
• Potosí – City in Bolivia