![]() Alkali feldspars Īlkali feldspars are grouped into two types: those containing potassium in combination with sodium, aluminium, or silicon and those where potassium is replaced by barium. K-feldspar is the final feldspar to crystallize from the magma. This defines the continuous Bowen's reaction series. Calcium-rich plagioclase is the first feldspar to crystallize from a cooling magma, but the plagioclase becomes increasingly sodium-rich as crystallization continues. The ratio of alkali feldspar to plagioclase feldspar, together with the proportion of quartz, is the basis for the QAPF classification of igneous rock. Albite is considered both a plagioclase and alkali feldspar. Only limited solid solution occurs between K-feldspar and anorthite, and in the two other solid solutions, immiscibility occurs at temperatures common in the crust of the Earth. Solid solutions between albite and anorthite are called plagioclase, or, more properly, plagioclase feldspar. Solid solutions between K-feldspar and albite are called alkali feldspar. ![]() ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |