Graulichite-(La), LaFe3+3(AsO4)2(OH)6, a new addition to the alunite supergroup from the Patte d'Oie mine, Bou Skour mining district, Morocco

The new mineral species graulichite-(La), ideally LaFe 3 3 + (AsO 4 ) 2 (OH) 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 0.34 Ce 0.20 Ca 0.11 Sr 0.07 Pb 0.05 K 0.04 ) Σ0.81 (Fe 2.16 3 + Al 0.84 Cu 0.20 ) Σ3.20 (As 1.23 P 0.39 S 0.37 ) Σ1.99 O 14 H 6.13 (domain #1) and (La 0.38 Ce 0.22 Sr 0.10 Ca 0.09 Pb 0.05 K 0.06 ) Σ0.90 (Fe 2.60 3 + Al 0.49 Cu 0.20 ) Σ3.29 (As 0.91 P 0.50 S 0.40 ) Σ1.81 O 14 H 6.53 (domain #2). Single-crystal unit-cell parameters are a=7.252(13) , c=16.77(3) Å, V=764(3) Å 3 , space group R -3 m . The eight strongest reflections in the observed X-ray powder diffraction pattern are ( d in Å, 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 3+ analogue of arsenoflorencite-(La).