Turquoise is a blue opaque semi-precious gemstone. The highest grades are "robin's egg blue," or the color of the blue sky. Inferior grades are greenish. Turquoise which fades in color is also inferior. Turquoise is a phosphate of aluminium with small quantities of copper and iron. The gem is slightly harder than glass. An example of high grade turquoise can be seen in this article about Bisbee Blue.
Turquoise pebble, one inch (2.5 cm) long. This pebble is greenish and therefore low grade.
In ancient times, turquoise was used by the Egyptians and was mined by them in the Sinai Peninsula. There are important deposits in Iran near Nishapur and in the American Southwest. Turquoise was more or less the national stone of Persia and was used extensively to decorate objects. Turquoise is used by Native American craftsmen, especially Navaho silversmiths.
Turquoise, along with coral is used extensively in the jewelry of Tibet and Mongolia. Turquoise is found in China and mined for the export trade, but not used for jewelry. A few carvings exist done in the same manner as jade carvings.
- Turquoise, Volume XII, Part II, Second Memoir, Third Memoir, Memoirs of the National Academy of Sciences, Joseph E. Pogue, The Rio Grande Press, Glorieta, New Mexico, hardback reprint, about 200 pages, ISBN 0-87380-056-7