Dear Mr. Karim,

apatite s.s.s. (Cl, F, CO3, OH) and APS minerals (aluminum phophate sulfate) are both placed on the opposite sides of the pH range. Apatite s.s.s. are stable at neutral to alkaline conditions, whereas APS minerals come into being at low pH /acidic conditions. For a more detailed description of the stability fields see below:

DILL, H.G. (2016) Kaolin: soil, rock and ore  From the mineral to the magmatic, sedimentary, and metamorphic environments.- Earth Sciences Reviews 161: 16-129.

DILL, H.G., WEBER, B. and BOTZ, R. (2013) Metalliferous duricrusts (“orecretes”) - markers of weathering: A mineralogical and climatic-geomorphological approach to supergene Pb-Zn-Cu-Sb-P mineralization on different parent materials.- Neues Jahrbuch für Mineralogie Abhandlungen, 190: 123-195.

DILL, H.G. (2001) The geology of aluminium phosphates and sulphates of the alunite supergoup: A review.- Earth Science Reviews, 53: 35-93.

Ca is ubiquitous and their is rarely a Ca limitation in the magmatic, metamorphic or sedimentary realm.

Best regards

H.G.Dill