Plagioclase

Plagioclase is a continuous series of feldspar minerals whose compositions range from sodium-rich albite to calcium-rich anorthite. It is a major constituent of many igneous rocks.

Feldspar: Feldspar is a group of rock-forming aluminosilicate minerals containing potassium, sodium, or calcium. Plagioclase is the sodium–calcium branch of this abundant mineral group.
Bowen's reaction series: Bowen's reaction series describes the order in which common silicate minerals crystallize as magma cools. Its continuous branch tracks changing plagioclase composition during magma cooling.
Igneous rock: An igneous rock forms when magma or lava cools and solidifies. Plagioclase is a common constituent used to describe and classify these rocks.
Oligoclase: Oligoclase is a sodium-rich plagioclase variety with an intermediate composition between albite and andesine. It exemplifies the sodium-rich part of the compositional series.
Albite: Albite is the sodium-rich end-member of the plagioclase series, with ideal composition NaAlSi₃O₈. It defines the series’ sodium-rich compositional endpoint.
Crystal fractionation: Crystal fractionation is the separation of crystallizing minerals from magma, changing the composition of the remaining melt. Removing early plagioclase crystals can shift a magma’s composition.
Anorthosite: Anorthosite is a coarse-grained igneous rock composed predominantly of plagioclase. This rock makes plagioclase its defining and dominant mineral.
Andesine: Andesine is a plagioclase variety intermediate in composition between oligoclase and labradorite. It represents an intermediate composition rather than either end-member.
Anorthite: Anorthite is the calcium-rich end-member of the plagioclase series, with ideal composition CaAl₂Si₂O₈. It defines the series’ calcium-rich compositional endpoint.
Zoning (geology): Zoning in a mineral is compositional variation between its core and outer growth zones. Plagioclase commonly records changing melt conditions in compositional zones.

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