Xanthiosite and aerugite

Abstract

Summary. Two nickel arsenates from South Terras mine, St. Stephen-in~Branne]l, Cornwall, have been shown to be identical with the minerals xanthiosite and aerugite, described by C. Bergemann in 1858, and with two synthetic products described by J. B. Taylor and R. D. Heyding (1958). Xanthiosite is pure golden- Early references to a tin-lode and an 'iron-lode' contain scant detail, and omit mention of the associated minerals actinolite, axinite, and garnet, with magnetite in the 'iron-lode', which is a metamorphic deposit in greenstone rather than a true lode. Mining of the iron deposit revealed in 1873 an intersection with a uranium lode, which was later developed as one of the main Cornish uranium deposits until it was exhausted about 35 years ago.The mineralization of this uranium lode, in common with that of other similar low-temperature Cornish cross-courses, is of the nickelcobalt-arsenic-bismuth-silver-uranium type. Some parts of the lode were rich in arsenopyrite and 1511ingite with smaller amounts of nickel and cobalt arsenides and accessory chalcopyrite, chaleocite, pyrite, and a little galena. This is the first record of 1511ingite at South Tetras, and

Structure of aerugite (Ni8.5As3O16) and interrelated arsenate and germanate structural series

“…It is probably isostructural with Mg3As20 8 (Krishnamachari & Calvo, 1973) and with the tetragonal form of Co3As208 (Gopal, Rutherford & Robertson, 1980). The X-ray powder pattern of synthetic aerugite closely corresponds to that of natural aerugite (Davis et al, 1965) and the unit-cell parameters (a = 5.952, c = 27.561 A, c/a = 4.631, obtained with a Guinier-Hagg camera and Cu K~q X-radiation) were similar to those of Mgs.sAs30~6. Single crystals were removed from the dish by soaking in distilled water for 24 h at room temperature.…”

“…Aerugite from South Terras mine, Cornwall (Davis et al, 1965) was too fine-grained for single-crystal X-ray study. Synthetic aerugite crystals were grown from a commercial amorphous nickel arsenate compound (with an Ni:As atomic ratio of 4:5 as determined by neutron activation analysis) heated in air in a platinum dish at about 1470K for l h. Initial melting and evaporation of arsenic oxide resulted in a mixture of a yellow microcrystalline phase and larger dark-green crystals of aerugite which were tabular with {001 }hex dominant.…”

“…From the work of Taylor & Heyding (1958) and Krishnamachari & Calvo (1970a), the mineral aerugite (Davis, Hey & Kingsbury, 1965) is isomorphous with the cobalt and magnesium arsenates, and the similar crystal chemistries of Mg 2+ and Ni 2+ in oxide compounds suggest that aerugite has the formula Nis. 5-ASaOl6.…”

Structures of orthorhombic and monoclinic Ni3(AsO4)2

“…Among the various structure types reported for the orthoarsenates M~(AsO4)2 (M= Mg, Mn, Co, Ni, Cu, Cd) (Krishnamachari & Calvo, 1973, 1970bKrishnamachari, 1970;Gopal, Rutherford & Robertson, 1980;Davis et al, 1965;Poulsen & Calvo, 1968;Hawthorne, 1986;Engle & Klee, 1970), the dimorphism of Ni3(AsO4) 2 described here is so far unique. On the one hand, the o-Ni3(AsO4)2 phase is the first example of an arsenate adopting this spinelrelated structure which is common among the orthovanadates M3(VO4)2 (M= Mg, Ni, Co, Cu, Zn) (Krishnamachari & Calvo, 1971;Sauerbrei et al, 1973;Shannon & Calvo, 1972).…”

“…Attempts to grow single crystals of the Ni3(AsO4)2 phase [i.e. xanthiosite, the other mineral identified by Davis et al (1965)] were unsuccessful using the same technique. Further experiments were therefore based on hydrothermal crystal growth using a powder of composition Ni3-(AsO4)2.8H20 as starting material.…”