IX. Class of Minerals

Phosphate minerals contain a tetrahedral phosphate anion group, which can be replaced by arsenate or vanadate anion groups, and their structure can also include chloride, fluoride, or hydroxide anions. Minerals in this class are numerous, but only a few species are more common in nature, such as minerals from the apatite group. We distinguish between primary phosphates, which form by crystallization from liquids, and secondary phosphates, which form by alteration (change) of primary phosphates. Phosphates can also occur in nature as rocks formed at low temperatures from organic material containing phosphorus.