Garavellite, FeSbBiS
4, 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 (VHN
50) is 206 kg/mm
2. 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.