The phosphate minerals, those containing the PO4 radical, have always been interesting to me.  This radical, with a negative three charge, is about the about the same size as the arsenate (AsO4) and vanadate (VO4) radicals and some minerals are involved in a solid solution relationship (see numerous previous posts). Members of the group also seem to have an affinity for the hydroxide ion, OH. Most of the phosphate minerals, with the exception of the apatite group, are rare or at least uncommon.  The phosphate radical also commonly attaches to metallic ions and produces, for example, wavellite and variscite (aluminum), turquoise (copper and aluminum), strengite (iron),  rockbridgeite (ironRead More →