Rhyolite

Classification：Igneous Rock

Rhyolite is a kind of igneous rock. It is an acid erupting rock of volcano. Its chemical composition is the same as granite. Because of its rapid cooling rate, the mineral is less than 69%, and the content of silica is greater than 69%. The speckles are mainly composed of potassium feldspar and quartz, crystal shape is square plate, glass luster, but jointed. Rocks are gray, pink or red brick, porphyritic texture and rhyotaxitic structure. Rhyolite is a kind of acidic extrusive rock with SiO content greater than 65% and rich in feldspar quartz minerals. It is widely distributed all over the world.

Summary：
Rhyolite is a volcanic extrusive rock equivalent to granite (granite). Most of the Rhyolite porphyritic structure, shows that the crystallization in the eruption had started. Sometimes when the magma is buried deep, the crystallization may have begun; in this case, the rock formed may be composed mainly of a single large crystal (speckle) that has developed well at the time of eruption.
The content of microcrystalline matrix in the final product may be too small to be seen under microscope. Such rocks (porphyry rocks) are easily mistaken for granite according to their hand specimens. However, the crystallization period of most Rhyolite is relatively short, so this rock is mainly composed of a few microcrystalline matrix or some glass matrix with a few speckles. The matrix is sometimes microtext like or blotch. The Rhyolite contains a glassy obsidian, pitchstone, perlite and pumice. Its chemical composition is the same as that of granites, which is intrusive rocks and extrusive rocks formed by allogenic magma. Gray or pale pink. Rhyolitic structure and porphyritic structure, glass structure, spherulitic structure, felsitic structure, micrographic structure is common. Phenocrysts are usually quartz and alkaline feldspar, sometimes with a small amount of plagioclase. The matrix is generally dense cryptocrystalline or vitreous. Most of the production is the rock mound. Devitrification obvious Rhyolite called rhyolite porphyry.

Regional distribution:
Rhyolite is widely distributed in all provinces of southeastern coastal China. Northern Liaoning, Inner Mongolia, Hebei, Shanxi, Shandong, Jilin and Heilongjiang also have distribution. Relating to mineral montmorillonite, kaolinite, pyrophyllite, alum and pyrite.
The Huangshi National Geopark, the Japanese ASU volcano, the Russian Sn Holt arling volcano belt] are affected by the subduction of the Western Pacific plate. In the eastern coastal area of China, there are also a large number of Jurassic and Cretaceous Rhyolite. They constitute a giant ancient fire belt of North South extension of more than 2000 km, the average width of about 400km. These Rhyolite are different in lithology and development. Under the action of external force erosion, many geomorphic landscapes with unique forms and rich types are often molded. Some areas become important tourist attractions because of these beautiful or magnificent landforms. Such as Zhejiang Yueqing's Yandang Mountain World Geopark, Jinyun's Xian Du National Geopark, Jilin Siping's Mountain Gate, National Geopark and so on.
Main components:
The chemical composition of Rhyolite is like granite. This correspondence means that there are at least some granites, and probably most of them are generated by magma. There are quartz, alkaline feldspar, Ordovician, biotite, hornblende or pyroxene in the phenocrysts of Rhyolite. If alkaline pyroxene or alkaline amphibole is a major dark mineral, the arcane feldspar is rare or not, and the feldspar is composed of large or all alkaline feldspar; this rock is called the alkali fluid rock. If alfeldite and alkaline feldspar occupy a prominent position in the speckles, the dominant dark silicate minerals will be black mica, and neither amphibole nor pyroxene, if any, will also be an alkaline variant; such lava is the quartz porphyry or "real" Rhyolite in most taxonomy.
Some differences between Rhyolite and granite are noteworthy. Muscovite is a common mineral in granite, but it is very rare in Rhyolite, or just as an alteration product. In most granites, alkaline feldspar is a micro - plagioclase (that is, micro - twill feldspar) with little sodium; however, in most Rhyolite, it is a feldspar and is often rich in sodium. Potassium is much more than that of sodium in granite. Unless it is the result of hydrothermal alteration, it is very rare in Rhyolite. Rhyolite is found in all parts of the world and in all geological years. Rhyolite is mainly confined to the mainland or near the edge of the continent, but elsewhere. It is reported that there are also small amounts of Rhyolite (or quartz trachyte) on oceanic islands away from any continent.

Classification:
Rhyolite can be divided into two series: calc alkaline and alkaline according to their geological characteristics and output.
1. calcium alkaline series
It is often associated with rhyolite, andesitic tuff, melted tuff and Ayama Ikyoo, and occurs in island arc, active continental margin and continental intraplate active belt. Is red, red meat, gray yellow and other colors, in addition to rhyolitic structure, as well as lithophysa. There are often porphyritic structures. The speckles are mainly quartz and permeable feldspar. Sometimes there are different numbers of plagioclase (mainly feldspar), a small amount of black mica, and occasionally the phenocryst. Under certain conditions, a small amount of cordierite, garnet and graphite can appear. Matrix for felsitic structure, spherulitic structure and glass structure.
2. alkaline series
It is often associated with alkali - fluid rock, alkali - long rough rock and alkaline basalt, which is produced in the stretching and rift stage of the continental margin active zone, and is the product of the later differentiation of the magma. Alkaline Rhyolite is usually green, greyish green, gray purple and gray white. It is a porphyritic structure. The phenocrysts are usually composed of sodium feldspar, anorthite or albite, with little or no quartz and a small amount of augite or augite. Matrix crystallites can be seen as nenite, sodium amphibole and sodium calcium amphibole. In addition to the matrix structure type calc alkaline Rhyolite, and rough structure and rough - felsitic structure.