An igneous rock has a large amount of feldspar. feldspar can be used to classify the rock based on which characteristic?

age
composition
origin
texture

Feldspar can be used to classify the rock based on composition.

Felsic rocks are the type igneous rocks which contain feldspar and quartz; and they are typically light in color. A rock which is classified as felsic is contains a high content of felsic minerals such as quartz, orthoclase, muscovite, plagioclase, etc.  

The common example of this type of rock is granite. Their chemical composition through the use of Total Alkali Silica determines the name of the felsic rocks. Felsic elements don't have enough magnesium, calcium and iron to form mafic rocks such as pyroxene or olivine.

answerformal;