Effenbergerite, BaCu[Si 4 O 10 ], a new mineral from the Kalahari Manganese Field, South Africa: description and crystal structure
1994; Cambridge University Press; Volume: 58; Issue: 393 Linguagem: Inglês
10.1180/minmag.1994.058.393.17
ISSN1471-8022
Autores Tópico(s)Crystal Structures and Properties
ResumoAbstract Effenbergerite, ideally BaCu[Si 4 O 10 ], structure determined by single crystal X-ray methods in space group P4/ncc , a = 7.442(2)Å, c = 16.133(5)Å, V = 893.50 Å 3 Z = 4, is a new mineral from the Wessels mine, Kalahari Manganese Field, South Africa. It is associated with native copper, calcite, quartz and clinozoisite within pectolite veinlets, embedded in a matrix of braunite, sugilite and hausmannite. Effenbergerite occurs as transparent blue platelets with perfect cleavage parallel to {001} in sizes up to 8.0 × 8.0 × 0.1mm. It has a pale blue streak, subconchoidal fracture, a calculated density of 3.52gcm −3 and an estimated Mohs' hardness of 4–5. Effenbergerite is uniaxial negative with ω = 1.633(2), ε = 1.593(2), strongly pleochroic from intense blue (ω) to nearly colourless (ε). The strongest lines in the X-ray powder diffraction pattern (with refined lattice parameters a = 7.440(1)Å, c = 16.133(2)Å) are: ( d obs / I obs / hkl ) (8.0624/100/002), (4.0325/39/004), (3.5443/29/104), (3.1998/44/114), (2.6892/21/006), (2.3943/41/116), (2.0169/34/008), (1.9466/22/108) and (1.4802/21/2.0.70). Effenbergerite is the natural analogue to synthetic BaCu[Si 4 O 10 ], isotypic with SrCu[Si 4 O 10 ] and CaCr[Si 4 O 10 ] as well as with the minerals cuprorivaite, CaCu[Si 4 O 10 ] and gillespite, BaFe[Si 4 O 10 ]. The structure consists of silicate sheets [Si 8 O 20 ] 8− parallel (001) formed by corner-linkage of silicate 4-membered rings. The copper(II) atom is nearly planar 4-coordinated; the barium atom has a distorted cubelike environment of oxygen atoms. The mineral is named for Dr. Herta S. Effenberger of the University of Vienna, Austria.
Referência(s)