The feldspar family is a continuous series of tectosilicates, if it is based on the same chemical composition for each crystal there are several variations within this family.
Indeed, their common base is to be oxides of aluminum and sodium, some will be composed in addition to that, of calcium while others will be of potassium.
Because of their chemical composition, these stones are however quite soft, they have indeed a hardness of 6.5 on the Mohs scale.
The various Feldspars :
Moonstone is an alkali feldspar micro-included with albite crystals which cause the opalescent blue highlights.
Sunstone is a potassium feldspar and is also called oligoclase. Known for its orange glittery appearance due to hematite inclusions, it can however also be found in gem quality in one deposit: Oregon in the USA.
Amazonite is an alkaline feldspar, generally green, more or less turquoise, with albite needles giving it a silvery sheen.
Labradorite is a potassium feldspar. It is famous for its brown background and its myriad of reflections ranging from golden to midnight blue through green and purple.