Arsenoflorencite-(La), a new mineral from the Komi Republic, Russian Federation: description and crystal structure

作者：Mills Stuart J^*; Kartashov Pavel M; Kampf Anthony R; Raudsepp Mati

来源：European Journal of Mineralogy, 2010, 22(4): 613-621.

DOI：10.1127/0935-1221/2010/0022-2043

• arsenoflorencite-(La)
• Grubependity Lake cirque
• Prepolar Ural
• Komi Republic
• crystal structure
• alunite supergroup
• lanthanum aluminium arsenate hydroxide
• new mineral

Arsenoflorencite-(La) [(sic)-(La)], ideally LaAl(3)(AsO(4))(2)(OH)(6), is a new mineral (IMA2009-078), from the Grubependity Lake cirque, Maldynyrd range, upper Kozhim River basin, Prepolar Ural, Komi Republic, Russia. It occurs in direct association with zircon, quartz, hematite, ardennite-(As), andalusite, anorthite, sericite, clinochlore, chernovite-(Y), manganiandrosite-(La), spessartine and monazite-gasparite-group minerals in Mn-rich nodules in metasediments. Arsenoflorencite-(La) forms orange- red to pink rhombohedral, pseudocubic or tabular crystals up to about 0.2 mm across. The dominant forms observed are {001} and {102}. The crystals have a vitreous lustre, are transparent to translucent, have a very light pink streak and are non-fluorescent. Mohs hardness is about 3.5 (estimated). The fracture is uneven and the tenacity is brittle. Arsenoflorencite-(La) has fair cleavage on {001}. Crystals are uniaxial (+), with the indices of refraction omega = 1.740(5) and epsilon = 1.750(5), measured in white light, and are nonpleochroic. The empirical formula (based on 14 O atoms) is: (La(0.56)Ce(0.18)Nd(0.12)Pr(0.04)Sr(0.09)Ca(0.03))(Sigma 1.02)(Al(2.94)Fe(0.06))(Sigma 3.00)(As(1.80)P(0.21))(Sigma 2.01)H(5.95)O(14). The simplified formula is LaAl(3)(AsO(4))(2)(OH)(6). Arsenoflorencite-(La) is trigonal, space group R (3) over barm, a = 7.0316(3), c = 16.5151(8) angstrom, V 707.16(5) angstrom(3) and Z = 3. The crystal structure was solved from single-crystal X-ray diffraction data and refined to R(1) = 0.0112 on the basis of 287 unique reflections with F(o) > 4 sigma F and R(1) = 0.0116 for all 293 reflections. The five strongest lines in the powder X-ray diffraction pattern are [d(obs) in angstrom, (I), (hkl)]: 2.982, (100), (113); 3.538, (55), (110); 1.914, (38), (303, 033); 2.211, (28), (122); 5.755, (27), (101). The name is for its relationship to florencite [and arsenoflorencite-(Ce)] with La as the dominant REE.

• 出版日期2010-8