Plagioclase

“Plagioclase” is the name of a group of feldspar minerals that form a solid solution series ranging from pure albite, to pure anorthite. Minerals in this series are a homogenous mixture of albite and anorthite. The names of the minerals in the series are arbitrarily given based upon their relative abundance of albite and anorthite. The minerals of the plagioclase series are listed in the table below along with their relative abundance of albite (Ab) and anorthite (An). The name “plagioclase” is frequently used instead of one of the more specific names in the table above. This is because the minerals of the plagioclase series are very similar and difficult to tell apart without laboratory testing. Thus the name “plagioclase” is commonly used in many field and classroom situations. https://www.mindat.org/min-3231.html https://geology.com/minerals/plagioclase.shtml