Volume 85, Numbers 3-4, 131-139, DOI: 10.1007/s00710-005-0083-7

Garavellite, FeSbBiS4, from the Caspari mine, North Rhine-Westphalia, Germany: composition, physical properties and determination of the crystal structure

L. Bindi and S. Menchetti

View Related Documents

Abstract

Garavellite, FeSbBiS4, was found in a sample of the mineralogical collection of the Natural History Museum of the University of Florence. The sample is from the Cu–Fe deposit of Caspari, Saverland, North Rhine-Westphalia, Germany. Garavellite occurs as very rare, elongated prismatic crystals up to 100 µm in length, spatially associated with large berthierite crystals, bismuthinite, chalcopyrite, and siderite. It does not contain inclusions of or intergrowths with other minerals. Macroscopically garavellite is grey in colour and shows a grey-black streak. The Vickers hardness (VHN50) is 206 kg/mm2. In plane-polarized incident light garavellite is grey in colour, with distinct bireflectance. Reflectance percentages for Rmin and Rmax are 33.8, 41.8 (471.1 nm), 33.3, 40.9 (548.3 nm), 32.7, 39.5 (586.6 nm), and 32.4, 38.8 (652.3 nm), respectively.
Garavellite is orthorhombic, space group Pnam, with the following unit-cell parameters: a = 11.413(1) Å, b = 14.164(1) Å, c = 3.759(1) Å, V = 607.7(2) Å3, and Z = 4. Electron microprobe analyses give the chemical formula Fe0.94Cu0.01As0.01Sb1.02Bi0.99S4.03. The crystal structure has been solved and refined to R = 2.38%. It consists of FeS6 octahedra forming edge-sharing chains parallel to [001] with the Sb3+ and Bi3+ cations inserted between the chains. The crystal-chemical relationships with berthierite as well as the different lone-pair stereochemical activities of antimony and bismuth in the two structures are discussed.

Fulltext Preview

Image of the first page of the fulltext document