Feldspar
A feldspar is a mineral based on double silicate of aluminum, potassium, sodium or calcium. Feldspars are from the tectosilicate family. There are many feldspars, the main ones being orthoclase, potassium, albite, sodium, and anorthite, calcium. The mixture of these last two gives the plagioclase series.
We can distinguish alkali feldspars, often translucent, whitish or pink and rich in alkalis (Na+, K+), from plagioclase which differ from the previous ones by the presence of calcium (Ca2+), and the absence of potassium (K+).
Feldspars form the largest group of minerals in the earth's crust. They are highly crystallized and have the property of forming twins and scratching glass.
In combination with other minerals, potassium feldspars (or alkaline or orthoclase) compose rather acidic rocks, such as syenites and granites (grained) or trachytes and rhyolites (microlithic). Plagioclase feldspars, for their part, make up, as far as grainy rocks are concerned, diorites, gabbros, more rarely tonalites and sometimes syenites. When they are found in microlithic rocks, they are most often andesites or basalts.
Source: Wikipedia, the free encyclopedia.
We can distinguish alkali feldspars, often translucent, whitish or pink and rich in alkalis (Na+, K+), from plagioclase which differ from the previous ones by the presence of calcium (Ca2+), and the absence of potassium (K+).
Feldspars form the largest group of minerals in the earth's crust. They are highly crystallized and have the property of forming twins and scratching glass.
In combination with other minerals, potassium feldspars (or alkaline or orthoclase) compose rather acidic rocks, such as syenites and granites (grained) or trachytes and rhyolites (microlithic). Plagioclase feldspars, for their part, make up, as far as grainy rocks are concerned, diorites, gabbros, more rarely tonalites and sometimes syenites. When they are found in microlithic rocks, they are most often andesites or basalts.
Source: Wikipedia, the free encyclopedia.