Turquoise

Turquoise is a translucent to opaque phosphate hydroxide rock whose chemical formula is CuO.3Al₂O₃.2P₂O5.9H₂O.

Turquoise can range from blue to green with more green indicating a higher iron content. Pyrite chunks and limonite veining can form along with inclusions of the host rock, which is often highly altered volcanic rock, to give character to each deposit.

Gem turquoise is cryptocrystalline and a 5-6 on the mohs scale of hardness. Turquoise can develop a green layer on the outside as it ages and dries out. Turquoise which is more porous is often stabilized and sold as lower grade material. 

Turquoise forms when copper oxides get intermixed in phosphate rich groundwater and settle as nodules or in veins. Turquoise primarily occurs in arid environments. 

Turquoise has been mined for over 6000 years. 

Turquoise is acid sensitive and should not be worn while handling harsh chemicals.