Amazonite

Amazonite (sometimes called "Amazon stone") is a green variety of microcline feldspar.

The name is taken from that of the Amazon River, from which certain green stones were formerly obtained, but it is doubtful whether green feldspar occurs in the Amazon area.

The modern amazonite is a mineral of limited occurrence. Formerly it was obtained almost exclusively from the area of Miyask in the Ilmen mountains , 50 miles southwest of Chehabinsk, Russia , where it occurs in granitic rocks. More recently, high-quality crystals have been obtained from Pike's Peak, Colorado, where it is found associated with smoky quartz, orthoclase, and albite in a coarse granite or pegmatite. Some other localities in the United States yield amazonite, and it is also found in pegmatite in Madagascar.

Because of its lively green colour, amazonite is sometimes cut and polished as a gemstone.

The colour has been attributed to the presence of copper, but, because it is removed by heat, it is likely to be due to some organic pigment, perhaps an organic salt of iron.

(original article from an old encyclopedia)