Guano phosphate minerals from

Apatites form an important series of minerals. They occur as a minor constituent of many igneous rocks, although a few large igneous deposits are known, like the Kola peninsular. Apatite is also present in most metamorphic rocks, especial crystalline limestone. Less well crystallised deposits of rather variable composition, usually referred to as rock phosphates or phosphorite, occur in large deposits, some of which were formed by the reaction between phosphatic solutions from guano and calcareous rock, or precipitated from sea water. 

---