Compounds of the crandallite-type: Synthesis, properties and thermodynamic data of pure crandallite and woodhouseite

Vibrational spectra of synthetic crandallite‐type minerals—optical and inelastic neutron scattering spectra

“…Crystal structures of natural crandallite 8 and goyazite (M D Sr; Pn D P) 9,10 were determined, and the D nuclei in synthetic goyazite-d 7 were localized by neutron diffraction. 11 The structures are basically the same as that of alunite, 12,13 KAl 3 (OH) 6 (SO 4 ) 2 , with the AlO 2 (OH) 4 octahedra (symmetry 2/m C 2h ) corner-linked to layers (Kagomé net) and HPO 4 and PO 4 groups attached on both sides of the layers in statistical distribution in crystallographically equivalent sites (formal symmetry 3m C 3v ).…”

“…at ambient and low temperatures (88 K) and far-IR spectra at room temperature. Comparisons with spectra of alunites, 16,17 woodhouseites, 18 monetite, 25 -28 CaHPO 4 , and apatite, 27 Ca 5 OH PO 4 3 , are helpful in the discussion of all types of spectra of crandallites, as are spectra of HPO 4 2 and PO 4 3 in solution. 29 -31 In contrast to the IR and Raman spectra of structurally ordered alunites with sharp (OH) doublets 16,17…”

“…9,10 Consequently, in crandallite, three pairs of -OH groups (and 3 ð 2 O atoms from HPO 4 /PnO 4 ) surround the displaced Ca ions at different distances (d(Ca-OH) 250.6, 267.8, 283.9 pm, respectively) 8 and therefore are no longer equivalent in their vibrational behaviour, whereas their equivalence in this respect is retained in goyazite. As a consequence of these different types of disorders, the selection rules derived for the ideal alunite structure (see preceding text) are expected to be softened in that non-equivalence, lifting of the degeneracies in general and different wavenumbers of the HPnO 4 and PnO 4 entities, should give rise to the appearance of more bands than predicted and to band broadening due to their overlapping.…”

“…In the frame of our work on minerals of and related to the alunite type, 1,2 we studied some synthetic crandallites, MAl 3 (OH) 6 (HPnO 4 )(PnO 4 ) (M D Ca, Sr, Ba, Pb; Pn D P, As) (short reports on the vibrational spectra, 3 thermoanalysis and thermodynamic data 4 have already been published), besides a sample of natural crandallite (M D Ca; Pn D P). 5 These crandallites belong to the alunite supergroup 6,7 and crystallize in space group R3m D 5 3d , No.…”

Gorceixita em Nefelina Sienitos do Stock Rio Pardo, Província Alcalina do Sul do Estado da Bahia, Nordeste do Brasil

“…Estes dados adicionamse a favor as descrições da literatura que relatam que a gorceixita cristaliza-se a baixa temperatura, associada a desestabilização da apatita. Os dados disponíveis na literatura [29,30] Os cálculos da fórmula estrutural dos cristais analisados foram efetuados com base de 10,5 oxigênios para a gorceixita anidra AB3(XO4)2 [4], sendo todo o ferro é expresso como Fe 3+ . Resultados representativos das análises químicas efetuadas nos cristais de gorceixita são apresentados na tabela 1.…”