In a previous thread, the nature of the orange crystals often found at La Ricamarie, Saint-Etienne, Loire, Rhône-Alpes, France was questionned. Such crystals are most often assigned to as Realgar and some Mindat contributors suggested these could be alternatively Alacranite, on the basis of their orange color and paragenesis (Alacranite is a typical species from burning coal dumps). Georges Favreau selected such an "alacranite-looking" specimen that was submitted for single-crystal X-ray diffraction (Univ. Rennes). These studies revealed the following parameters (data collection at 100 K; Rint = 0.05): 9.82 / 9.29 / 8.88 / 90 / 102.03 / 90 in the space group P2/c. Such structural features actually correspond to the natural analogue of formula beta-As4S4, a species somewhat related to Alacranite but definitively a distinct one, which was recently identified (though still unnamed) around Lihir Island in Papua New Guinea. At this stage, only this very specimen, selected for its orange color and apparent similarity with Alacranite, was analyzed; it is not yet defined whether or not this species is largely spread at this locality.
For more details on the complex structural chemistry of Alacranite-related species, see (a) Alacranite, As8S9: structural study of the holotype and re-assignment of the original chemical formula Am. Miner. 2003, 88, 1796-1800; (b) ALACRANITE, As4S4: A NEW OCCURRENCE, NEW FORMULA, AND DETERMINATION OF THE CRYSTAL STRUCTURE, P. C. Burns, J. B. Percival, Canad. Miner., 2001, 39, 809-818. (both references can be easily accessed via the RUFF project; follow the link on Alacranite Mindat page)
Georges Favreau and Jean-Francois Carpentier

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