Plagioclase Feldspar Granite

Rather than referring to a particular mineral with a specific chemical composition plagioclase is a continuous solid solution series more properly known as the plagioclase feldspar series.

Plagioclase feldspar granite.

Plagioclase is the name of a group of feldspar minerals that form a solid solution series ranging from pure albite na alsi 3 o 8 to pure anorthite ca al 2 si 2 o 8 minerals in this series are a homogenous mixture of albite and anorthite. Hornblende and biotite are the commonest mafic minerals however muscovite is also frequently encountered. Granite is classified according to the qapf diagram for coarse grained plutonic rocks and is named according to the percentage of quartz alkali feldspar orthoclase sanidine or microcline and plagioclase feldspar on the a q p half of the diagram. Cloud granite morton gneiss and wausau.

This was first shown by the german mineralogist johann friedrich christian hessel 1796 1872 in 1826. They are major constituents in a wide range of intrusive and extrusive igneous rocks including granite diorite gabbro rhyolite andesite and basalt. The names of the minerals in the series are arbitrarily given based upon their relative abundance of albite and anorthite. They are importantly dominant minerals in most igneous rock.

True granite according to modern petrologic convention contains both plagioclase and alkali feldspars. Plagioclase is a series of tectosilicate framework silicate minerals within the feldspar group. The plagioclase feldspar subgroup consists of a continuous mineral series that is arbitrarily subdivided into six mineral categories whose composition varies from being relatively pure sodium aluminum silicate albite to a relatively pure calcium aluminum silicate anorthite.