Amazonite, also known as Amazonstone, is a green tectosilicate , a variety of the potassium feldspar called microcline Its chemical formula which is polymorphic.
Its name is taken from that of the Amazon River , from which green stones were formerly obtained, though it is unknown whether those stones were amazonite. Although it has been used for over two thousand years, as attested by archaeological finds in Egypt and Mesopotamia, no ancient or medieval authority mentions it. It was first described as a distinct mineral only in the 18th century.
Green and greenish-blue varieties of potassium feldspars which are predominantly triclinic are designated as amazonite. It has been described as a "beautiful crystallized variety of a bright verdigris-green" and as possessing a "lively green colour." It is occasionally cut and used as a gemstone