Plagioclase

Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Plagioclase is an important series of tectosilicate minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series (from the Greek "oblique fracture", in reference to its two cleavage angles). The series ranges from albite to anorthite endmembers (with respective compositions NaAlSi3O8 to CaAl2Si2O8), where sodium and calcium atoms can substitute for each other in the mineral''s crystal lattice structure. Plagioclase in hand samples is often identified by its polysynthetic twinning or ''record-groove'' effect.