What is a phosphate in mineralogy ?
Phosphates : definition
Phosphates constitute the major subclass of the large mineralogical class of phosphates - arsenates - vanadates ; they are built from tetrahedral anionic groups (PO4)3- and different cations.
A mineralogical group, apatite, Ca5(PO4)3(OH,F,Cl) largely dominates this class by its abundance and its geological and economic importance. It alone concentrates more than 90% of the phosphorus in the earth's crust.
Equivalent tetrahedral units (AsO4)3- and (VO4)3- are the basis of arsenates and vanadates. P5+, As5+, and V5+ are easily replaced in anionic groups, there are transition terms between phosphates, arsenates and vanadates. Pyromorphite, Pb5(PO4)3Cl, mimetite Pb5(AsO4)3Cl and vanadinite Pb5(VO4)3Cl, for example, form extended (but not complete) series between them.
The term "phosphates" also applies in a somewhat abusive way to sedimentary rocks essentially formed of phosphates (in the form of fluorapatite and carbonate-apatite) : the phosphorites.
A mineralogical group, apatite, Ca5(PO4)3(OH,F,Cl) largely dominates this class by its abundance and its geological and economic importance. It alone concentrates more than 90% of the phosphorus in the earth's crust.
Equivalent tetrahedral units (AsO4)3- and (VO4)3- are the basis of arsenates and vanadates. P5+, As5+, and V5+ are easily replaced in anionic groups, there are transition terms between phosphates, arsenates and vanadates. Pyromorphite, Pb5(PO4)3Cl, mimetite Pb5(AsO4)3Cl and vanadinite Pb5(VO4)3Cl, for example, form extended (but not complete) series between them.
The term "phosphates" also applies in a somewhat abusive way to sedimentary rocks essentially formed of phosphates (in the form of fluorapatite and carbonate-apatite) : the phosphorites.
Apatite from Anemzy, Imilchil, Er Rachidia Province, Morocco
Pyromorphite from Les Farges, Corrèze, France
Fossilized shark tooth from Moroccan "phosphates"