AbstractInfra‐red absorption spectra, differential thermal and differential thermogravimetric curves, and some newX‐ray diffraction data are presented for synthetic or natural specimens of variscite, metavariscite, strengite, phosphosiderite, barrandite, leucophosphites, taranakites, wavellite and synthetic phosphates of composition KAl2(PO4)2(OH),2H2O, H8(NH4,K)Fe3(PO4)6, 6H2O and H4CaFe2(PO4)4, 5H2O. Infra‐red spectra of berlinite, phosphotridymite and two other anhydrous forms of A1PO4are also given. The infra‐red spectra show that variscite and metavariscite have the structure A1PO4, 2H2O and not A1(OH)2, H2PO4, and serve to indicate the porportion of A1/Fe in the barrandites (Fe, A1)PO4, 2H2O. Leucophosphite, KF2(PO4)2(OH), 2H2O is shown to dehydrate reversibly to a monohydrate and then to an anhydrous product still containing the hydroxy