Turquoise is a copper aluminium phosphate mineral with a hardness of 5 to 6. Its striking blue color is caused by copper. And the greenish shades of turquoise are because of iron its crystal structure is triclinic, and it is usually composed of submicroscopic crystals making the stone opaque. The name turquoise is derived from the French pierre turquoise meaning Turkish stone. This is because the trade routes through which turquoise reached Europe from the mines in central asia went through turkey and venetian merchants often bought the stone in Turkish bazzars.