The mineral tooeleite is without doubt an arsenic(III) mineral, as declared by Morin et al. [Morin, G., Rousse, G., Elkaim, E., 2007. Crystal structure of tooeleite, Fe(6)(AsO(3))(4)SO(4)(OH)(4) center dot 4H(2)O, a new iron arsenite oxyhydroxy-sulfate mineral relevant to acid mine drainage. American Mineralogist 92, 193-197], whereas in previously published work by Cesbron and Williams [Cesbron, F.P., Williams, S.A., 1992. Tooeleite, a new mineral from the US Mine, Tooele County, Utah. Mineralogical Magazine 56, 71-73] the arsenic was considered to contain arsenic(V). There has also been suggestion that in certain acid mine drainage there is evidence of bacterial mediation to form nano-particular and poorly ordered iron(III)-arsenic(III)/(V) hydroxy sulfates which may be efficient bioremediators, as in Duquesne et al. [Duquesne, K., Lebrun, S., Casiot, C., Bruneel, O., Personne, J.-C., Leblanc, M., Elbaz-Poulichet, F., Morin, G., Bonnefoy, V., 2003. Immobilization of arsenite and ferric iron by Acidithiobacillus ferrooxidans and its relevance to acid mine drainage. Applied Environmental Microbiology 69, 6165-6173], and Morin et al. [Morin, G., Juillot, F., Bruneel, O., Personne, J.-C., Elbaz-Poulichet, F., Leblanc, M., Ildefonse, Ph., Calas, G., 2003. Bacterial formation of tooeleite and mixed As(III)/(V)-Fe(III) gels in the Carnoules acid mine drainage. France. A XANES XRD, and SEM study. Environmental Science and Technology 37, 1705-1712]. Tooeleite was originally described by Cesbron and Williams (1992) as a new mineral from the US Mine at Gold Hill in Tooele County, Utah, USA, where gold had previously been mined for many years. These authors suggested a formula in which the arsenic was present as arsenic(V). The mineral occurrences at that US Mine had been earlier described by Nolan [Nolan, T.B., 1935. The Gold Hill Mining District. U.S.G.S. Professional Paper 177 pp.]. The work reported here now confirms that the mineral tooeleite is in fact an arsenic(III) compound which can be easily prepared in the laboratory by precipitation from pure components in aqueous solutions at temperatures up to at least 90 degrees C. Other conclusions reached here are supported with the results from analysis of solutions and solids, as well as by X-ray diffraction analysis, thermogravimetric-differential thermal analysis, scanning electron microscopy, and also by X-ray photoelectron spectroscopy analysis. (c) 2007 Elsevier Ltd. All rights reserved.