Feldspar!

FELDSPAR

it is the name of a group of rock-forming minerals which make up as much as 60% of the earth's crust. crystallize from magma in both intrusive & extrusive rocks, & they can also occur as compact minerals as veins & are also present in many types of metamorphic rock . rock formed entirely of plagioclase Feldspar is known as northosite. they are also found in many types of sedimentary rock. it is typically reddish / pale pink in color, & has a hardness of 60 the mohs scale.

feldspar is derived from the german word feld, field, spat ; a rock that does not contain ore. feldspar refers to minerals that contains feldspar.

COMPOSITION :
this group of minerals consists of framework or tectosilicates . composition of major elements in common feldspar can be expressed in term of 3 endmembranes.

K-feldspar endmembranes = KAlSi3O8
Albite endmembranes = NaAlSi3O8
Anorthite endmembranes = CaAl2Si2O8

- sodium solution between K-feldspar & albit are called alkali feldspar.
- solid solution between albite & anorthite are called plagioclase.
- sanidine, orthoclase, microline refer to polymorphs of K-feldspar.

- sanidine is stable at the highest temperature
- microline at the lowest perthite is typical texture in alkali feldspar, due to exsolution of contrasting alkali feldspar compositions during cooling of an intermediate composition. the perthitic texture in the alkali feldspar of many granites are coarse enough to be visible to the naked eye.

USES :
- feldspar is common raw material in the production of ceramics.
- feldspar are used for thermoluminescence dating & optical dating in earth science & archeology.
- feldspar is often an anti-eating agent used in powedered forms of non-dairy creams.