Graulichite-.sub.6, a new addition to the alunite supergroup from the Patte d'Oie mine, Bou Skour mining district, Morocco

• Published in: European journal of mineralogy (Stuttgart) 2022-06, Vol.34 (3), p.365
• Main Authors: Biagioni, Cristian, Ciriotti, Marco E, Favreau, Georges, Mauro, Daniela, Zaccarini, Federica
• Format: Article
• Language: English
• ISSN: 0935-1221

The new mineral species graulichite-(La), ideally LaFe33+(AsO.sub.4).sub.2 (OH).sub.6, has been discovered in the Patte d'Oie mine, Bou Skour mining district, Morocco. It occurs as yellow rhombohedral crystals, up to 0.1 mm in size, with a resinous luster, associated with malachite, agardite-(La), conichalcite, and a still undetermined REE carbonate. Crystals are chemically zoned and two homogeneous domains were identified, corresponding to the empirical chemical formulae (calculated on the basis of 6 cations per formula unit, assuming the occurrence of 14 O atoms) (La.sub.0.34 Ce.sub.0.20 Ca.sub.0.11 Sr.sub.0.07 Pb.sub.0.05 K.sub.0.04).sub.Σ0.81 (Fe2.163+Al.sub.0.84 Cu.sub.0.20).sub.Σ3.20 (As.sub.1.23 P.sub.0.39 S.sub.0.37).sub.Σ1.99 O.sub.14 H.sub.6.13 (domain #1) and (La.sub.0.38 Ce.sub.0.22 Sr.sub.0.10 Ca.sub.0.09 Pb.sub.0.05 K.sub.0.06).sub.Σ0.90 (Fe2.603+Al.sub.0.49 Cu.sub.0.20).sub.Σ3.29 (As.sub.0.91 P.sub.0.50 S.sub.0.40).sub.Σ1.81 O.sub.14 H.sub.6.53 (domain #2). Single-crystal unit-cell parameters are a=7.252(13), c=16.77(3) Ã, V=764(3) Ã.sup.3, space group R-3m. The eight strongest reflections in the observed X-ray powder diffraction pattern are (d in Ã, visually estimated intensity): 5.86, medium; 3.045, strong; 2.511, medium-weak; 2.239, medium; 1.960, medium-weak; 1.813, medium-weak; 1.689, medium-weak; 1.478, medium. Graulichite-(La) belongs to the dussertite group within the alunite supergroup. It is the La analogue of graulichite-(Ce) and the Fe.sup.3+ analogue of arsenoflorencite-(La).