Auriacusite, Fe[superscript 3+]Cu[superscript 2+]AsO[subscript 4]O, the first M[superscript 3+] member of the olivenite group, from the Black Pine mine, Montana, USA
- CMN
Auriacusite, ideally Fe{sup 3+}Cu{sup 2+}AsO{sub 4}O, is a new arsenate mineral (IMA2009-037) and the Fe{sup 3+} analogue of olivenite, from the Black Pine mine, 14.5 km NW of Philipsburg, Granite Co., Montana, USA. It occurs lining quartz vughs and coating quartz crystals and is associated with segnitite, brochantite, malachite, tetrahedrite and pyrite. Auriacusite forms fibrous crystals up to about 5 {micro}m in width and up to about 100 {micro}m in length, which are intergrown to form fibrous mats. Individual crystals are a brownish golden yellow, whilst the fibrous mats are ochreous yellow. The crystals have a silky lustre and a brownish yellow streak. Mohs hardness is about 3 (estimated). The fracture is irregular and the tenacity is brittle. Auriacusite crystals are biaxial (+), with {alpha} = 1.830(5), {beta} = 1.865(5) and {gamma} = 1.910(5), measured using white light, and with 2V{sub meas.} = 83(3){sup o} and 2V{sub calc.} = 84.6{sup o}. Orientation: X = a, Y = c, Z = b. Crystals are nonpleochroic or too weakly so to be observed. The empirical formula (based on 5 O atoms) is (Fe{sub 1.33}{sup 3+}Cu{sub 0.85}Zn{sub 0.03}){sub {Sigma}2.21}(As{sub 0.51}Sb{sub 0.27}Si{sub 0.04}S{sub 0.02}Te{sub 0.01}){sub {Sigma}0.85}O{sub 5}. Auriacusite is orthorhombic, space group Pnnm, a = 8.6235(7), b = 8.2757(7), c = 5.9501(5) {angstrom}, V = 424.63(6) {angstrom}{sup 3}, Z = 4. The five strongest lines in the powder X-ray diffraction pattern are [d{sub obs} in {angstrom}/(I)/hkl]: 4.884/(100)/101, 001; 2.991/(92)/220; 2.476/(85)/311; 2.416/(83)/022; 2.669/(74)/221. The crystal structure was solved from single-crystal X-ray diffraction data utilising synchrotron radiation and refined to R{sub 1} = 0.1010 on the basis of 951 unique reflections with F {alpha} > 4{sigma}F. Auriacusite is identified as a member of the olivenite group with Fe{sup 3+} replacing Zn{sup 2+} or Cu{sup 2+} in trigonal bipyramidal coordination. Evidence suggests that auriacusite is an intermediate member between olivenite and an as yet undescribed Fe{sup 3+}Fe{sup 3+}-dominant member. The name is derived from the Latin auri (golden yellow) and acus (needle), in reference to its colour and crystal morphology.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- OSTI ID:
- 1022260
- Journal Information:
- Miner. Petrol., Vol. 99, Issue (1-2) ; 2010; ISSN 0930-0708
- Country of Publication:
- United States
- Language:
- ENGLISH
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