Turquoise is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminium, Even the finest of turquoise is fracturable, reaching a maximum hardness of just under 6, or slightly more than window glassThe lustre of turquoise is typically waxy to subvitreous, and transparency is usually opaque, but may be semitranslucent in thin sections.

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. For at least 2,000 years, the region once known as Persia has remained an important source of turquoise.

Since at least the First Dynasty (3000 BCE), and possibly before then, turquoise was used by the Egyptians and was mined by them in the Sinai Peninsula. The turquoise occurs as vein or seam fillings, and as compact nuggets;

Hardness and richness of colour are two of the major factors in determining the value of turquoise; while colour is a matter of individual taste, generally speaking, the most desirable is a strong sky to "robin's egg" blue (in reference to the eggs of the American Robin. Whatever the colour, turquoise should not be excessively soft or chalky.