Almeidaite, Pb(Mn,Y)Zn-2(Ti,Fe3+)(18)O-36(O,OH)(2), a new crichtonite-group mineral, from Novo Horizonte, Bahia, Brazil

作者：Menezes Filho Luiz A D; Chukanov Nikita V; Rastsvetaeva Ramiza K; Aksenov Sergey M; Pekov Igor V; Chaves Mario L S C; Richards R Peter; Atencio Daniel; Brandao Paulo R G; Scholz Ricardo; Krambrock Klaus; Moreira Roberto L; Guimaraes Frederico S; Romano Antonio W; Persiano Aba C; de Oliveira Luiz C A; Ardisson Jose D

来源：Mineralogical Magazine, 2015, 79(2): 269-283.

DOI：10.1180/minmag.2015.079.2.06

• almeidaite
• new mineral
• crichtonite group
• crystal structure
• chemical composition
• Novo Horizonte
• Bahia
• Brazil

Almeidaite (IMA 2013-020), ideally Pb(Mn,Y)Zn-2(Ti,Fe3+)(18)O36(O,OH)(2), from Novo Horizonte, Bahia, Brazil, occurs in association with quartz, rutile, anatase, hematite, kaolinite, muscovite, xenotime-(Y) and bastnaesite-(La). Almeidaite forms isolated, black, opaque, sub-metallic, platy crystals flattened on [0001], measuring up to 30 mmx30 mmx6 mm in size, dominated by the basal pinacoid {0001}, which is bounded by various, mostly steep, rhombohedra and the hexagonal prism {11 (2) over bar0}. Most of the crystals are multiply twinned, with non-planar contact surfaces that are approximately parallel to the c axis. The streak is brown. Reflectance values are [(R-o, R-e) lambda (nm)]: (12.78, 15.39) 470; (12.86, 15.43) 546; (12.91, 15.55) 589; (13.04, 15.75) 650. The empirical formula is (Pb0.59Sr0.12Ca0.04La0.03)(Sigma 0.78)(Mn0.54Y0.46)(Sigma 1.00)Zn-1.43(Ti13.02Fe4.983+)(Sigma 18.00)(Fe0.323+Mn0.15)(Sigma 0.47) [O-37.18(OH)(0.82)](Sigma 38.00). It is trigonal, space group R (3) over bar, with the unit-cell parameters a = 10.4359(2), c = 21.0471(4) angstrom, V = 1985.10(7) angstrom(3) and Z = 3. The crystal structure was solved (R-1 = 0.039) using 2110 unique reflections with I > 3 sigma(I). Almeidaite is a member of the crichtonite group with Pb dominant in the A site (with 12-fold coordination) and Zn dominant in the T site (with 4-fold coordination). It is a Zn analogue of senaite and a Pb analogue of landauite. The mineral is named after Professor Fernando Flavio Marques de Almeida (1916-2013).

• 出版日期2015-4