The crystal chemical role of Fe-Mn substitution in the epidote family

Abstract The pearceite-polybasite group of minerals, general formula [M6T2S7][Ag9CuS4] with M = Ag, Cu; and T = As, Sb, show a crystal structure which can be described as the succession, along the c axis, of two pseudo-layer modules: a [M6T2S7]2– A module layer and a [Ag9CuS4]2+ B module layer. Copper is present in one structural position of the B module layer and replaces Ag in the only fully occupied M position of the A module layer. When the Cu content is >4.00 a.p.f.u., the structural position of the A module layer becomes Cu-dominant and, consequently, the mineral deserves its own name. In this paper we report the crystal-chemical characterization of two Cu-rich members exhibiting the 111 unitcell type (corresponding to the Tac polytype). One sample (space group (P )m1, a 7.3218(8), c 11.8877(13) Å, V 551.90(10) Å3, Z = 1) having As >Sb and with the structural position of the A module layer dominated by Cu, has been named cupropearceite and the other sample (space group (P3̄)m1, a 7.3277(3), c 11.7752(6) Å, V 547.56(8) Å3, Z = 1) having Sb >As has been named cupropolybasite. Both the new minerals and mineral names have been approved by the IMA-CNMNC.

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Stabilizing role of lithium in structures of complex oxide compounds as an instrument for crystal chemical design

Journal of Structural Chemistry ◽

10.1007/s10947-009-0193-x ◽

2009 ◽

Vol 50 (S1) ◽

pp. 78-85 ◽

Cited By ~ 2

Author(s):

S. F. Solodovnikov ◽

E. G. Khaikina ◽

Z. A. Solodovnikova

Keyword(s):

Complex Oxide ◽

Crystal Chemical ◽

Chemical Design

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The structure of antimonian dussertite and the role of antimony in oxysalt minerals

Mineralogical Magazine ◽

10.1180/002646199548277 ◽

1999 ◽

Vol 63 (1) ◽

pp. 17-26 ◽

Cited By ~ 12

Author(s):

U. Kolitsch ◽

P. G. Slade ◽

E. R. T. Tiekink ◽

A. Pring

Keyword(s):

Hydrogen Bonding ◽

Electron Microprobe ◽

Structure Refinement ◽

Bond Valence ◽

Crystal Chemical ◽

Coordination Polyhedra ◽

Space Group ◽

Bond Lengths ◽

The Mean

AbstractThe structure of antimonian dussertite, (AsO4)2(OH,H2O)6, has been refined in space group R3̄m with a 7.410(3), c 17.484(4) Å, Z = 3, to R = 3.2 % and Rw = 3.7 % using 377 observed reflections with I ≥ 3 σ(I). The structure is of the alunite-type and consists of sheets of corner-sharing (Fe3+,Sb5+)O6 octahedra parallel to (0001). The substitution of Sb5+ for Fe3+, and not for As5+, is unambiguously demonstrated not only by the structure refinement but also by electron microprobe analyses and crystal-chemical considerations. The icosahedrally coordinated Ba cations occupy cavities between pairs of octahedral sheets and are surrounded by six O atoms from the AsO4 tetrahedra and six O atoms from the (Fe3+,Sb5+)O6 octahedra. The mean bond lengths for the various coordination polyhedra are As-O 1.684(3) Å, (Fe,Sb)-O 2.004(1) Å, and Ba-O 2.872(2) Å. A hydrogen-bonding network is modelled using bond-valence calculations. The dussertite sample investigated is the first member of the crandallite group found to contain substantial Sb.

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