TY - JOUR
T1 - Coulsellite, CaNa3AlMg3F14, a rhombohedral pyrochlore with 1:3 ordering in both A and B sites, from the Cleveland Mine, Tasmania, Australia
AU - Mumme, William
AU - Grey, Ian
AU - Birch, W
AU - Pring, Allan
AU - Bougerol, Catherine
AU - Wilson, N
PY - 2010/5
Y1 - 2010/5
N2 - Coulsellite, CaNa3AlMg3F14, from the Cleveland tin mine at Luina, western Tasmania, has a rhombohedral distortion of the cubic pyrochlore A2B2X6Y structure, with a = 7.1756(1) Å, α = 59.867(1)°, space group R3̄m, Z = 1. The corresponding hexagonal cell parameters are a = 7.1620(1) Å, c = 17.5972(3) Å. The crystals are multiply twinned about threefold axes of the pseudocubic cell. The structure was determined using X-ray data collected on a twinned crystal and refined to Robs = 0.027 for 452 observed reflections with I > 2σ(I). The structure is possibly unique among published structures of pyrochlore-like minerals in having full 1:3 ordering of Ca:Na in the A sites and Al:Mg in the B sites. Transmission electron photomicrographs show a nanodomain structure due to twinning on a scale of ∼5 nm.
AB - Coulsellite, CaNa3AlMg3F14, from the Cleveland tin mine at Luina, western Tasmania, has a rhombohedral distortion of the cubic pyrochlore A2B2X6Y structure, with a = 7.1756(1) Å, α = 59.867(1)°, space group R3̄m, Z = 1. The corresponding hexagonal cell parameters are a = 7.1620(1) Å, c = 17.5972(3) Å. The crystals are multiply twinned about threefold axes of the pseudocubic cell. The structure was determined using X-ray data collected on a twinned crystal and refined to Robs = 0.027 for 452 observed reflections with I > 2σ(I). The structure is possibly unique among published structures of pyrochlore-like minerals in having full 1:3 ordering of Ca:Na in the A sites and Al:Mg in the B sites. Transmission electron photomicrographs show a nanodomain structure due to twinning on a scale of ∼5 nm.
KW - 1:3 cation ordering in CaNa AlMg F
KW - New fluoride mineral
KW - Rhombohedral pyrochlore
KW - Structure determination
UR - http://www.scopus.com/inward/record.url?scp=77953201085&partnerID=8YFLogxK
U2 - 10.2138/am.2010.3360
DO - 10.2138/am.2010.3360
M3 - Article
VL - 95
SP - 736
EP - 740
JO - American Mineralogist
JF - American Mineralogist
SN - 0003-004X
IS - 5-6
ER -