Picrite

Classification：Igneous Rock

Picrite is a rare rock type, which is composed of peridotite and pyroxene.

Features：
Picrite belongs to the ultrabasic eruption rock. The rocks are dark green or gray green. Mineral composition is mainly composed of olivine and pyroxene, with small amount of plagioclase and very few hornblende. Among them, about 50 to 75% olivine. Accessory minerals include magnetite, chromite and apatite. The rocks are cryptic, microcrystalline, or small round olivine embedded in pyroxene. Picrite is seldom distributed in nature, and few independent rock masses are formed, which constitute part of the basic extrusive rock mass.

Mineral composition:
Picrite is one of the ultrabasic lava. Mineral composition is mainly composed of pyroxene and olivine, with a small amount of basic plagioclase and metallic minerals. The composition is similar to the deep formed pyroxene peridotite. It has microcrystalline structure. Such as porphyritic structure, known as the "picrite porphyrite".

Naming reasons:
The term "Picrite" was first applied to a rich class of coarse basalt or basalt, including olivine and pyroxene. It is also used to represent volcanic rocks corresponding to feldspar peridotite or alkaline peridotite, as well as olivine variants representing gabbro and boiling greenstone. A group of rocks determined by chemical composition to be SiO2<47% and Na2O+K2O>18%. The mineral components are pyroxene (less than 40%), olivine (more than 40%), sometimes a small amount of basic plagioclase (<10%) and hornblende, and the accessory minerals are ilmenite, magnetite and apatite. The igneous rock, which is equivalent to peridotite composition (titanium pyroxene 34%, olivine 31%, brown amphibole 25%, accessory mineral 5%, alkaline glass 5%), has also been named Picrite. The word "Hui Yun" peridotite in China is originally translated from the Greek language pikros, meaning bitterness, which means the content of Magnesium Oxide is high. Some people think that the volcanic rock equivalent to the eclogite is called Picrite, while the volcanic rock with the composition equivalent to the pure peridotite is called the maigi rock.

Classification and distribution:
Picrite can be generally divided into: Olivine Picrite, olivine pyroxene Picrite and pyroxene Picrite3 species. Picrite is often formed in continental overflow basalt or oceanic spillway basalt areas related to mantle plume activities, such as the Mount Emei basalt province of our country, and a small amount of Picrite formed in subduction related island arc environments, such as the Kamloops region of Great Britain, Canada.