The most abundant
group of mineral
s in the earth
. Quite a lot of them have been used for jewelry
; most of them are translucent
but a few form transparent crystal
s. It can take chemical analysis to tell exactly what particular type of feldspar a material is, since they all are in the 6 to 6.5 range on the Mohs hardness scale
and have other characteristics in common.
Feldspars are divided into subfamilies such as the plagioclase (including labradorite, spectrolite) and the orthoclase (including moonstone, adularia) and the oligoclase (including sunstone) families.