pigeonite

This leads to a miscibility gap between pigeonite and augite compositions.

At lower temperatures, pigeonite is unstable relative to augite plus orthopyroxene.

Quartz is absent, as are orthopyroxene and pigeonite.

Olivine may also be a phenocryst, and when present, may have rims of pigeonite.

With declining temperature, augite may exsolve lamellae of pigeonite and/or orthopyroxene.

They are mostly composed of Ca-poor pyroxene, pigeonite, and Ca-rich plagioclase (anorthite).

It was discovered in 1982 during the chemical analysis of The North Haig olivine pigeonite achondrite (ureilite).

In tholeiitic basalt, pyroxene (augite and orthopyroxene or pigeonite) and calcium-rich plagioclase are common phenocryst minerals.

These phenocrysts are pyroxenes (augite and pigeonite), plagioclases, opaque crystals such as titanomagnetite or ilmenite, and occasionally some olivine.

Orthopyroxene or pigeonite may also be present in tholeiitic basalt, and olivine, if present, may be rimmed by either of these calcium-poor pyroxenes.

The Funagata volcano is made up of andesite, which is easily distinguished from the pigeonite basalt that erupted from Mout Kurohana.

At relatively high temperatures, there is a miscibility gap between diopside and pigeonite, and at lower temperatures, between diopside and orthopyroxene.

Primary (magmatic) mineral species also encountered in komatiites include olivine, the pyroxenes augite, pigeonite and bronzite, plagioclase, chromite, ilmenite and rarely pargasitic amphibole.

It forms complete solid solution series with hedenbergite (FeCaSiO) and augite, and partial solid solutions with orthopyroxene and pigeonite.

Olivine tholeiite has augite and orthopyroxene or pigeonite with abundant olivine, but olivine may have rims of pyroxene and is unlikely to be present in the groundmass.

Occasionally widespread assemblages like garnet + orthopyroxene, ternary feldspars, (F-Ti) pargasite or metamorphic inverted pigeonite are taken as typical indicators of UHT metamorphism.

In slowly cooled intrusive igneous rocks, pigeonite is rarely preserved, but textural evidence of its breakdown to orthopyroxene plus augite may be present, as shown in the accompanying microscopic image.