Phosphate Family

Phosphates are rocks which are primarily composed of phosphorous. Phosphorous can be from an inorganic or organic source with much being from seawater. 

Well known phosphate gems include:

Apatite -  usually hydroxyapatite, fluorapatite and chlorapatite (written as Ca10(PO4)6(OH)2, Ca10(PO4)6F2 and Ca10(PO4)6Cl2) - Occurs in many colors with a hardness of 5

Lazulite - Magnesium Iron Aluminium Phosphate - Dark blue with a hardness of 5.5 to 6

Turquoise - Copper Aluminum Phosphate - Blue to green with moderate hardness of a 5-6

Variscite - Hydrous Aluminum Phosphate - Green to Green/Yellow often softer than turquoise