Turquoise (the name derived from an Old French word for "Turkish", because the mineral was first brought to Europe from Turkey, from the mines in historical Khorasan Province of Iran) is a hydrous phosphate of copper and aluminium mineral.
Characteristically, turquoise almost never forms single crystals and all of its properties are highly variable. Colour is as variable as the mineral's other properties, ranging from white to a powder blue to a sky blue, and from a blue-green to a yellowish green. The blue is attributed to copper while the green may be the result of either iron impurities (replacing aluminium) or dehydration. Turquoise might lack the sparkle and clarity of transparent coloured gemstones like ruby, emerald and sapphire, but it is rare and valuable and its multi-layered history has been prized as a gem and ornamental stone for thousands of years owing to its unique hue.