Arsenate Mineral

Arsenic minerals are widely distributed throughout the world and small amounts of the free element have also been found. Common... 

The difference in mineralogy of the Kuroko and present-day back-arc deposits are (1) metastable phases such as native sulfur, wurtzite, and amorphous silica are poor in the Kuroko deposits (2) arsenic minerals such as jordanite, tetrahedrite-tennantite, native arsenic, and realgar are common in the present day back-arc deposits (Okinawa Myojinsho Knoll Caldera), but rare in Kuroko deposits except tetrahedrite-tennantite (3) secondary minerals such as cerussite and covellite are common in present day back-arc deposits (e.g., Okinawa, Myojinsho Knoll Caldera) (4) Dendritic texture is common in the present day back-arc deposits. 

Micro-XRD confirms that secondary phases are generally aggregates of micro-or nano-scale crystallites, or in some cases amorphous or short-range ordered. Arsenic-mineral associations within... 

Compounds of arsenic are extremely widespread. The black crust often found on native arsenic is a mixture of arsenic and arsenious oxide, AsaOs. This oxide frequently accompanies other arsenical minerals and occurs in two crystalline varieties, arsenolite (cubic), usually as minute octahedra in capillary crystallisations or in stellar aggregates, and claudetite8 (monoclinic), in thin plates resembling selenite. Both forms are lustrous and may be transparent to translucent, colourless to white. 

Arsenic occurs also in a great variety of other minerals, generally as mixed arsenides and sulphides of the heavy metals or as metallic arsenites and arsenates, anhydrous and hydrated. The more common of these are listed below, with their approximate composition. They are to be found in small quantities widely scattered over Europe,12 Asia, America and Australia. Thus arsenical minerals in great variety13 are found in the blendes and lead glances of the Eastern Alps, the former... 

Various attempts have been made to employ electrolytic methods for the extraction of arsenic from arsenical minerals. Thus Siemens and Halske 3 suggested the treatment of sulphide ores with sulphides or hydrosulphides of the alkali metals so that the arsenic passed into solution as a double sulphide or thioarsenite, thus ... 

Arsenates. Minerals containing the arsenate radical. As04. 

Common arsenic minerals and other solid arsenic compounds 2.4.2.1 Introduction... 

Geologists define a mineral as a naturally occurring, crystalline, and inorganic solid. Although liquids, gases, synthetic materials, amorphous substances, and organic compounds may contain arsenic, they are not minerals. Arsenic minerals include rhombohedral elemental arsenic, arsenolamprite, pararsenolamprite, and over 320 inorganic compounds (Foster, 2003), 39. Chapter 3 discusses the natural occurrences and potential environmental impacts of several of the more common arsenic minerals. 

Arsenopyrite (FeAsS), an arsenosulfide, is the most common arsenic mineral on Earth (Welch et al., 2000), 597. The mineral occurs in a variety of hydrothermal deposits and some metamorphic and intrusive igneous rocks Table 2.5 (Klein, 2002), 369. As mentioned earlier in this chapter, the crystalline structure of... 

Basalts and gabbros are the dominant igneous rocks in oceanic crusts. In rare circumstances, the mafic rocks of the oceanic crust (e.g. at the Mid-Atlantic Ridge) contain various arsenic minerals, including... 

Schaufelberger, F.A. (1994) Arsenic minerals formed at low temperatures, in Arsenic in the Environment Part I Cycling and Characterization (ed. J.O. Nriagu), John Wiley Sons, Ltd, New York, pp. 403-15. 

Ray, A.K. (1999). Chemistry of arsenic and arsenic minerals relevant to contamination of groundwater and soil from subterranean source. Everyman s Science, 35(1). 

Dogan, M. and Dogan, A.U. (2007) Arsenic mineralization, source, distribution, and abundance in the Kutahya region of the western Anatolia, Turkey. Environmental Geochemistry and Health, 29(2), 119-29. 

Samecka-Cymerman, A. and Kempers, A.J. (1994) Aquatic bryophytes as bioindicators of arsenic mineralization in Polish and Czech Sudety Mountains. Journal of Geochemical Exploration, 51(3), 291-97. 

Arsenopyrite and loellingite are both arsenic minerals that can be smelted to produce elemental arsenic. Both elemental arsenic and arsenic trioxide (As203) are produced commercially the latter is the raw material for the production of numerous arsenic compounds. Elemental arsenic is used to make alloys with lead and copper. Arsenic compounds have a number of uses, including... 

A wide variety of minerals was observed however, this discussion will emphasize the mode of occurrence of the As-bearing phases both trivalent and pentavalent arsenic minerals were observed. 

The application of lead isotope analyses to provenancing almost pure copper artifacts seems relatively straightforward in most instances, but what of arsenical copper and tin bronze alloys In principle, the arsenic in arsenical copper may have been derived from high-arsenic minerals (such as tennantite or basic copper arsenates) containing lead of a different isotopic composition from that of the copper ore used to produce the copper. However, absolutely no archaeological or other evidence of proves that this was ever done in the Bronze Age Aegean. On the contrary, at Kythnos definite evidence shows that arsenical copper was produced in EBII times from arsenical copper ores of variable (sometimes zero) arsenic content but of uniform lead isotope composition. 

Arsenic has a very well-developed mixed-valence chemistry with sulfur in part to the occurrence of several of these species as arsenic minerals. Tetraarsenic trisulfide, AS4S3, is orange-yeUow and occurs as the mineral dimorphite which is found in a and fi forms. The solid-state structure of both the a and fi forms exhibit C3, symmetry (15), differences arise due to crystal packing effects. ... 

Migdisov A. A. and Bychkov A. Y. (1998) The behaviour of metals and sulphur during the formation of hydrothermal mercury-antimony-arsenic mineralization, Uzon caldera, Kamchatka, Russia. J. Volcanol. Geotherm. Res. 84, 153-171. 

The average crustal abundance of arsenic is 1.5mgkg . The element is strongly chaloco-phile. Approximately 60% of natural arsenic minerals are arsenates, 20% sulfides and sulfosalts, and the remaining 20% are arsenides. 

Solid-phase As can be found in many different forms in aquifer sediments examples include (1) stoichiometric arsenic minerals (2) solid solution of arsenic in minerals or x-ray amorphous phases from trace (< 1000 ppm) to atom percent levels (3) coprecipitation of As with minerals during their formation and (4) adsorption of As on particle surfaces. This section gives a brief background on the macroscopic and spectroscopic techniques that are commonly used for ascertaining As species in these phases. 

Of the greater than 320 known As minerals, fewer than 10 are commonly identified in the environment, and with the exception of scorodite, the most commonly reported arsenic minerals are arsenic oxides or arsenic sulfides (Welch et ah, 1988). Very little structural or thermodynamic data exists for arsenate and arsenite minerals, and even less spectroscopic information. Hess and Blanchar (1976) determined solubility products for synthetic Al,... 

As mineralisation at depth, is a prerequisite for high As concentrations in geothermal fluids. Most reservoir fluids are undersaturated with respect to arsenopyrite and other arsenic minerals (Ballantyne and Moore, 1988) and hence As leaching, rather than As precipitation, is predicted to occur in the reservoir. 

Figure 5. Arsenic mineral precipitates at the Waiotapu geothermal field, Taupo Volcanic Zone, NZ a) An As- and Sb-rich sulphide precipitate in Champagne Pool, b) Yellow orpiment in a small hot. spring.

Waste piles from former bedrock mining in the area are found to contain up to 30% As, the majority in secondary arsenate minerals, particularly scorodite (Williams et ah, 1996). Alluvial soils also contain up to 5000 mg kg As. In these, Fordyce et al. (1995) concluded that some 20% of the As was present in crystalline iron oxides, with the remainder assumed to be in sulphate mineral phases or other oxidised products. 

Early work by the Public Health Engineering Department, Government of West Bengal (PHED, 1991) reported that arsenic is present as adsorbed ions on clay particles/quartz particles and also as primary arsenic mineral(s) . X-ray diffraction of the arseniferous horizons was reported to have shown traces of arsenopyrite. The reported As contents of sediments from Kochua, West Bengal were extremely low, <0.2 mg kg" in all cases, and below the detection limit (probably about O.I mg kg ) in the sandy horizons. 

Dunning, G. E., 1988, Calcium arsenate minerals. New to the Getchell mine, Nevada Mineralogical Record, v. 19, p. 253-257. 

Rochette, E. A., li, G. C., and Fendorf, S. E., 1998, Stabdity of arsenate minerals in sod under bioticady generated reducing conditions Sod Science Society of America Journal,... 

Raman spectroscopy was used to characterise a range of arsenate minerals of the vivianite type.589 IR and Raman spectra were assigned on the basis of factor group analysis for Cd2As207, Table 13.590 Ab initio calculations have given values for the vibrational wavenumbers for As4Ofi.591... 

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