TY - JOUR
T1 - Jahn-Teller Distortion and Cation Ordering
T2 - The Crystal Structure of Paratooite-(La), a Superstructure of Carbocernaite
AU - Krivovichev, Sergey V.
AU - Panikorovskii, Taras L.
AU - Zolotarev, Andrey A.
AU - Bocharov, Vladimir N.
AU - Kasatkin, Anatoly V.
AU - Škoda, Radek
PY - 2019/6
Y1 - 2019/6
N2 - The crystal structure of paratooite-(La) has been solved using crystals from the type locality, Paratoo copper mine, near Yunta, Olary Province, South Australia, Australia. The mineral is orthorhombic, Pbam, a = 7.2250(3) angstrom, b = 12.7626(5) angstrom, c = 10.0559(4) angstrom, V = 927.25(6) angstrom(3), and R-1 = 0.063 for 1299 unique observed reflections. The crystal structure contains eight symmetrically independent cation sites. The La site, which accommodates rare earth elements (REEs), but also contains Sr and Ca, has a tenfold coordination by seven carbonate groups. The Ca, Na1, and Na2 sites are coordinated by eight, eight, and six O atoms, respectively, forming distorted CaO8 and Na1O(8) cubes, and Na2O6 octahedra. The Cu site is occupied solely by copper and possess a distorted octahedral coordination with four short (1.941 angstrom) and two longer (2.676 angstrom) apical Cu-O bonds. There are three symmetrically independent carbonate groups (CO3)(2-) with the average bond lengths equal to 1.279, 1.280, and 1.279 angstrom for the C1, C2, and C3 sites, respectively. The crystal structure of paratooite-(La) can be described as a strongly distorted body-centered lattice formed by metal cations with (CO3)(2-) groups filling its interstices. According to the chemical and crystal-structure data, the crystal-chemical formula of paratooite-(La) can be described as (La0.74Ca0.11Sr0.07)(4)CuCa(Na0.75Ca0.15)(Na-0.63)(CO3)(8) or REE2.96Ca1.59Na1.38CuSr0.28(CO3)(8). The idealized formula can be written as (La,Sr,Ca)(4)CuCa(Na,Ca)(2)(CO3)(8). The structure of paratooite is a 1 x 2 x 2 superstructure of carbocernaite, CaSr(CO3)(2). The superstructure arises due to the ordering of the chemically different Cu2+ cations, on one hand, and Na+ and Ca2+ cations, on the other hand. The formation of a superstructure due to the cation ordering in paratooite-(La) compared to carbocernaite results in the multiple increase of structural complexity per unit cell. Therefore, paratooite-(La) versus carbocernaite represents a good example of structural complexity increasing due to the increasing chemical complexity controlled by different electronic properties of mineral-forming chemical elements (transitional versus alkali and alkaline earth metals).
AB - The crystal structure of paratooite-(La) has been solved using crystals from the type locality, Paratoo copper mine, near Yunta, Olary Province, South Australia, Australia. The mineral is orthorhombic, Pbam, a = 7.2250(3) angstrom, b = 12.7626(5) angstrom, c = 10.0559(4) angstrom, V = 927.25(6) angstrom(3), and R-1 = 0.063 for 1299 unique observed reflections. The crystal structure contains eight symmetrically independent cation sites. The La site, which accommodates rare earth elements (REEs), but also contains Sr and Ca, has a tenfold coordination by seven carbonate groups. The Ca, Na1, and Na2 sites are coordinated by eight, eight, and six O atoms, respectively, forming distorted CaO8 and Na1O(8) cubes, and Na2O6 octahedra. The Cu site is occupied solely by copper and possess a distorted octahedral coordination with four short (1.941 angstrom) and two longer (2.676 angstrom) apical Cu-O bonds. There are three symmetrically independent carbonate groups (CO3)(2-) with the average bond lengths equal to 1.279, 1.280, and 1.279 angstrom for the C1, C2, and C3 sites, respectively. The crystal structure of paratooite-(La) can be described as a strongly distorted body-centered lattice formed by metal cations with (CO3)(2-) groups filling its interstices. According to the chemical and crystal-structure data, the crystal-chemical formula of paratooite-(La) can be described as (La0.74Ca0.11Sr0.07)(4)CuCa(Na0.75Ca0.15)(Na-0.63)(CO3)(8) or REE2.96Ca1.59Na1.38CuSr0.28(CO3)(8). The idealized formula can be written as (La,Sr,Ca)(4)CuCa(Na,Ca)(2)(CO3)(8). The structure of paratooite is a 1 x 2 x 2 superstructure of carbocernaite, CaSr(CO3)(2). The superstructure arises due to the ordering of the chemically different Cu2+ cations, on one hand, and Na+ and Ca2+ cations, on the other hand. The formation of a superstructure due to the cation ordering in paratooite-(La) compared to carbocernaite results in the multiple increase of structural complexity per unit cell. Therefore, paratooite-(La) versus carbocernaite represents a good example of structural complexity increasing due to the increasing chemical complexity controlled by different electronic properties of mineral-forming chemical elements (transitional versus alkali and alkaline earth metals).
KW - CARBONATE
KW - DEPOSIT
KW - LA
KW - MINERALS
KW - PARATOO
KW - RARE-EARTHS
KW - STABILITY
KW - archetype
KW - carbocernaite
KW - carbonate
KW - cation array
KW - cation ordering
KW - copper
KW - crystal structure
KW - paratooite-(La)
KW - rare earth elements
KW - superstructure
KW - Archetype
KW - Paratooite-(La)
KW - Carbocernaite
KW - Rare earth elements
KW - Copper
KW - Crystal structure
KW - Cation ordering
KW - Carbonate
KW - Superstructure
KW - Cation array
UR - http://www.scopus.com/inward/record.url?scp=85070219445&partnerID=8YFLogxK
UR - http://www.mendeley.com/research/jahnteller-distortion-cation-ordering-crystal-structure-paratooitela-superstructure-carbocernaite
U2 - 10.3390/min9060370
DO - 10.3390/min9060370
M3 - Article
AN - SCOPUS:85070219445
VL - 9
JO - Minerals
JF - Minerals
SN - 2075-163X
IS - 6
M1 - 370
ER -