Although the average proportion of phosphorus in Australian coals is similar to that of P in world coal deposits generally (around 0.05% or 500 ppm), a number of individual seams have phosphorus contents above this average. Ply-by-ply studies of selected seams indicate that P is typically abundant in only a few sub-sections or plies; the remaining parts of the seam, even in high-phosphorus coals, commonly have significantly lower phosphorus levels. The bulk of the phosphorus in Australian coals is present as crystalline mineral particles, although some of these may be only a few micrometres in diameter and intimately associated with the organic components. X-ray diffraction of low-temperature oxygen-plasma ash residues, combined with EDAX investigations of polished sections of coal under the scanning electron microscope, show that the phosphorus usually occurs either as apatite or as a solid-solution of Sr, Ba and Ca aluminophosphates that represent minerals of the goyazite-gorceixite-crandallite group. Both apatite and a range of aluminophosphate minerals can occur in the one coal sample, although one phosphate mineral variety is usually the dominant component. The apatite and the aluminophosphates most commonly occur as infillings in the pore spaces and cell cavities of inertinite macerals. They sometimes occur alone, but in many cases are intimately associated with kaolinite and possibly quartz. Later-formed veins filled with either apatite or aluminophosphate minerals also occur in some coal seams, particularly in the more vitrinite-rich sub-sections. These typically cross-cut the pore-filling accumulations. The phosphorus that formed these minerals was probably derived mainly from phospho-proteins in the organic matter of the original peat deposits, although volcanic debris, shells or faecal matter may also have acted as phosphorus sources. The P was apparently released in a more soluble form during plant decay, and then reprecipitated with other available ions in the pores of appropriate parts of the peat bed. Factors such as pH and metal availability were probably critical in determining whether apatite or aluminophosphates were formed. Where they occur, phosphate-bearing veins probably represent material remobilised from earlier-formed accumulations and precipitated from groundwaters after the coals had essentially reached their present rank.