The Phosphate class is made up of minerals with a basic chemical unit of tetrahedral (PO4) groups with the Phosphorus atom at the center and Oxygens at each of the four corners. The overall unit charge is a negative three (3-). This chemical group can be combined with metal ions in a one to one ratio, or usually in more complex combinations, with other ions such as Hydroxide groups (OH), Uranyl groups (UO2), a halogen, or even water molecules. This gives rise to many possible permutations and therefore Phosphates are usually highly complex minerals.

The typical phosphate is vitreous to dull, often strongly coloured, above average in density, average in hardness (4-7) and low in refractive index, unless metals such as Lead are present. All the remaining properties are highly variable. Many interesting and beautiful mineral specimens come from this class but although over 300 recognised Phosphates are known, only few are common. Some are primary minerals in igneous rocks and in pegmatities, including Triphylite and Lithiophilite, whereas others are secondary species formed by weathering processes in near-surface environments. The latter include Reddingite, Sicklerite and Stewartite.

The Arsenate class almost perfectly mirrors the Phosphates in many ways including structure, diversity and properties. The only major difference is the Arsenate, (AsO4) 3-, ion replacing the Phosphate ion. The ions have the same charge and roughly the same size and therefore can usually substitute for each other in the structure of minerals. In fact, many minerals exist as a solid solution series between species that contain the Phosphate ion as their main anion and those that contain Arsenate. Good examples of this duality are Mimetite and Pyromorphite.

Another structurally related class are the Vanadates, which contain the structurally similar (VO4) 3- vanadate ion. The structure is tetrahedral with the Vanadium atom at the centre and four Oxygen atoms at each of the tetrahedron corners. The three negative charges are distributed evenly over the four Oxygens and are balanced by metal ions. The combined structure is characterised by relatively dense crystals. There are around 50 recognised minerals but most of them are extremely rare. Because Vanadates have an affinity for forming compounds with heavy metal ions, they are an important source of Uranium.