Last December we looked at Zircon and Tanzanite, but there is another stunning December birthstone we would like to talk to you about today. Turquoise is found in only a few places on earth. Mainly dry and barren regions where acidic, copper-rich groundwater seeps downward and reacts with minerals that contain phosphorous and aluminium. The result of this process is a porous, semi translucent to opaque compound of hydrated copper and aluminium phosphate. Turquoise is a great example of an opaque coloured stone that can be marketed both as a gem for jewellery and as an ornamental material.