Turquoise has been - and still is - known by many names, but the word turquoise was probably derived sometime in the 16th century from the French word for Turkish (Turquois) or dark-blue stone (pierre turquin). This may have arisen from a slight misunderstanding of where it came from: turquoise does not occur in Turkey but was traded at Turkish bazaars to Venetian merchants who brought it to Europe.
Turquoise is a copper aluminium phosphate with a hardness of 6, i.e. considerably softer than quartz. In Nature, it occurs in the whole range of hues from sky blue to grey-green, and it is mostly found in places where there is a high concentration of copper in the soil. However, turquoise is only really turquoise in the very best quality; mostly, the colour is paler, or bluish-green or greenish. The blue colour is created by copper, the green by bivalent iron and a certain amount of chrome. Often, the material has veins or blotches running through it, which are brown, light grey or black depending on where it was found. These lively, more or less regular patterns are known as 'turquoise matrix'. The crystals are microscopically small and can hardly ever be recognised with the naked eye. As a rule, turquoise occurs as a filling in veins or crevices, or in the form of nuggets. The most well known deposits are in the USA, Mexico, Israel, Iran, Afghanistan and China. The most beautiful turquoises, in a splendid light blue, come from deposits in the north of Iran. This blue turquoise turns green when heated.
Turquoise is rarely faceted. Usually, it is cut into cabochons or beads, or into some more imaginative shape.