Feldspattiluokat

Feldspattiluokat refers to the classification of feldspars, a group of abundant rock-forming minerals in the Earth's crust. Feldspars are tectosilicates with the general formula XAl(Si,Al)3O8, where X is typically a large cation such as potassium (K), sodium (Na), or calcium (Ca). The classification is primarily based on the chemical composition and the crystal structure of these minerals.

There are two main series within the feldspar group: the alkali feldspars and the plagioclase feldspars. Alkali feldspars are characterized by their solid solution series between potassium feldspar (KAlSi3O8) and albite (NaAlSi3O8). This series includes minerals like orthoclase, microcline, sanidine, and anorthoclase. Plagioclase feldspars form a continuous solid solution series between albite (NaAlSi3O8) and anorthite (CaAl2Si2O8). This series is divided into several distinct mineral species based on the molar percentage of albite and anorthite, including albite, oligoclase, andesine, labradorite, bytownite, and anorthite.

The distinction between alkali feldspars and plagioclase feldspars is crucial in petrology for understanding the origin and evolution of igneous rocks. Their optical properties, hardness, and cleavage are also important characteristics used in their identification in hand specimens and under a microscope. The presence and relative proportions of different feldspar types can provide significant clues about the geological environment in which a rock formed.