Greenish-colored potassium feldspar is uncommon, but specimens are readily available in the mineral trade. The traditional variety of green feldspar is amazonite, a greenish microcline feldspar. Green orthoclase feldspar is exceedingly rare, and is known from few localities on Earth. Some may be tempted to call this stuff amazonite, but it isn’t. Amazonite only refers to (it’s supposed to refer to) green microcline. Orthoclase feldspar is KAlSi3O8 (potassium aluminosilicate), an abundant rock-forming mineral and a polymorph of microcline (also KAlSi3O8). Published chemical analysis indicates that the green coloration is due to lead impurity.
Here’s a large mass of Precambrian-aged green orthoclase feldspar, from what is traditionally the only known occurrence in the world. This is from the Broken Hill Block of western New South Wales in Australia.
Green orthoclase feldspar (field of view ~9 cm across) from Southern Cross, ~11-12 km N of the city of Broken Hill, Broken Hill Block, far-western New South Wales, southeastern Australia.
Collected & generously donated by Molly Tannian.