TURQUOISE is a blue-green mineral (in composition it corresponds to magnesium-aluminum phosphate). It is formed by secondary precipitation from waters containing copper, aluminum and phosphorus in sediments, especially in sandstone or volcanics rich in cavities. Its name is derived from the word "turquois" (Turkish), not from its turquoise color - it was imported into Europe from Persia via Turkey. It occurs mainly in the Sinai Peninsula, New Mexico, Arizona and Nevada. TYRKENITE is a colored stone (most often colored howlites or magnesites, which do not have a nice natural color). The coloration is permanent (there is no risk of coloring the skin or clothing), the layman is usually not able to visually distinguish Tyrkenite from Turquoise, so it is used as a cheaper substitute for Tyskys.