Effenbergerite, BaCu[Si₄O₁₀], a new mineral from the Kalahari Manganese Field, South Africa: description and crystal structure

Abstract

Effenbergerite, ideally BaCu[Si4010], structure determined by single crystal X-ray methods in space group P4/ncc, a=7.442(2).~, c= 16.I33(5)A, V = 893.50 ,~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 x 8.0 x 0.1mm. It has a pale blue streak, subconchoidal fracture, a calculated density of 3.52gcm -3 and an estimated Mobs' hardness of 4-5. Effenbergerite is uniaxial negative with to= 1.633(2), = 1.593(2), strongly pleochroic from intense blue (to) to nearly colourless (e). Tl~.e strongest lines in the X-ray powder diffraction pattern (with refined lattice parameters a=7.

Heat capacity, thermal expansion and heat transport in the Han Blue (BaCuSi4O10): Observation of structural phase transitions

“…The rings are linked together by squareplanar coordinated copper, forming double copper-silicate [CuSi 4 O 10 ] n layers parallel to the (001) plane, which are joined by barium ions that are positioned between these layers. The blue color of BaCuSi 4 O 10 compounds comes from crystal-field splitting of the Cu 2+ d orbitals in their square-planar coordination [6,10,11].…”

“…The electronic, optical and structural properties of BaCuSi 4 O 10 have been well investigated in the room temperature region [5,6,10,11,12,13,14]. Further knowledge of the physical properties may prove valuable due to increasing technological interest.…”

Wesselsite, SrCu[Si4O10], a further new gillespite-group mineral from the Kalahari Manganese Field, South Africa

“…Synthesis experiments by the method proposed by Pabst (1959) at temperatures of 800~ from various mixtures of BaCO3, SrCO3, CuO and SiO2 might yield suitable material for single crystal X-ray studies of ordering phenomena. (Chakoumakos et al, 1993), (4) effenbergerite, BaCu[Si4Olo] (Giester and Rieck, 1994), (5) synthetic SrCr[Si4Olo] (Miletich and Allan, 1996) …”

“…These grains were embedded between sugilite crystals and resembled effenbergerite. BaCu[Si40,d, which had recently been described from this locality (Giester and Rieck, 1994). As the assemblage of the matrix was distinctly different.…”

“…60, pp. 795-798 Copyright the Mineralogical Society yielded crystals of effenbergerite (Giester and Rieck, 1994). Since approval of wesselsite the authors became aware of two further samples (both with approximate dimensions 5 x 5 x 2 cm) with a mineral content slightly different from the type specimen.…”