The most common minerals in the world are the feldspars, which make up nearly 60% of the earth's crust. Given the ubiquity of feldspar, it is somewhat surprising that there are so few feldspar gemstones. By contrast, another very common mineral, quartz, has as least a dozen well-known gemstone varieties, including amethyst, citrine, tiger's eye, chalcedony and agate.
There are two main subgroups of feldspar that produce gem-quality material: the potassium feldspars and the plagioclases, a series that ranges from calcium to sodium feldspars. Among the feldspar gemstones are moonstone, orthoclase, amazonite, andesine, labradorite and sunstone.
Amazonite, moonstone and orthoclase are all potassium feldspars. They have a hardness of 6 to 6.5 on the Mohs scale, and a vitreous luster. Moonstone is a very well-known gemstone, but orthoclase and amazonite are not.
Amazonite is a gemstone variety of green microcline. It is named after the Amazon river in Brazil, though surprisingly no deposits have been found in that location. The story is that some green stones were found in the Amazon river area, but mineralogists believe that there is no green feldspar in that area, though there are deposits elsewhere in Brazil.
The lively green or blue-green color of amazonite can be quite beautiful when polished. Since amazonite is an opaque stone, it is usually fashioned as cabochons. It is a medium-hard material, rating 6 to 6.5 on the Mohs scale, so it is not ideally suited to rings. But it makes very attractive earrings and pendants.
For many years, the source of amazonite's color was a mystery. Many people assumed the color was due to traces of copper because copper compounds often have blue and green colors. More recent studies suggest that the blue-green color results from small quantities of lead and water in the feldspar.
Amazonite is found in relatively few locations in the world. At one time it was found almost exclusively in Russia, in the Ilmen mountains. More recently, deposits have been found in the USA (Colorado), Brazil and Madagascar.
Amazonite is said to calm one's emotions and soothe nerves, and to enhance creativity and the ability to express oneself. Perhaps the strongest recommendation for its metaphysical power is that Amazonite is said to make your married life happier.