Feldspar
Feldspar is the most abundant mineral group in the Earth's crust — a family of aluminosilicates of potassium, sodium and calcium. It spans the potassium feldspars (orthoclase, microcline) and the plagioclase series (albite through anorthite), and is a primary building block of granite and many other rocks. Collectors prize varieties such as amazonite (green microcline), moonstone and labradorite.
About Feldsparextended article
Feldspar — the crust's default mineral
Feldspars make up more of Earth's continental crust than any other mineral family. The group splits into two branches: the alkali feldspars — orthoclase and microcline, including the turquoise-green variety amazonite — and the plagioclase series running from sodium-rich albite to calcium-rich anorthite.
The collector varieties
Collectors mostly meet feldspar through its show-off varieties: amazonite's saturated blue-green, moonstone's billowy adularescence, and labradorite's electric flash of blue-gold iridescence (labradorescence) caused by light interference within microscopic exsolution layers.
Identification notes
Two cleavage directions at roughly right angles and hardness 6 are the quick field tests; plagioclase often adds fine parallel striations on cleavage faces that alkali feldspars lack.
Frequently asked questions
What is Feldspar?
Feldspar is the most abundant mineral group in the Earth's crust — a family of aluminosilicates of potassium, sodium and calcium. It spans the potassium feldspars (orthoclase, microcline) and the plagioclase series (albite through anorthite), and is a primary building block of granite and many other rocks. Collectors prize varieties such as amazonite (green microcline), moonstone and labradorite.
What crystal system does Feldspar belong to?
Feldspar crystallises in the Monoclinic crystal system.
Is Feldspar rare?
As a collector mineral, Feldspar is generally considered common.
References & databases
Mindat.org is the world’s largest open mineralogy database. Our descriptions are written independently and fact-checked.
