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TitleNevadaite, (Cu2+,?,Al,V3+)6[Al8(PO4)8F8](OH)2(H2O)22, a new phosphate mineral species from the Gold Quarry mine, Carlin, Eureka County, Nevada: description and crystal structure
AuthorCooper, M A; Hawthorne, F C; Roberts, A C; Foord, E E; Erd, R C; Evans, H T, Jr; Jensen, M C
SourceCanadian Mineralogist vol. 42, no. 3, 2004 p. 741-752,
Alt SeriesGeological Survey of Canada, Contribution Series 2004127
PublisherMineralogical Association of Canada
Mediapaper; on-line; digital
File formatpdf
AreaEureka County; Carlin; Nevada; United States of America
Lat/Long WENS-116.5000 -116.0000 40.0000 39.0000
Subjectsmineralogy; metallic minerals; supergene deposits; gold; mines; phosphate; crystalline phases; crystallography
Illustrationstables; schematic diagrams; diagrams
ProgramCanada Research Chairs
ProgramNSERC Natural Sciences and Engineering Research Council of Canada
AbstractNevadaite, (Cu2+, \'01, Al, V3+ )6 (PO4)8 F8 (OH)2 (H2O)22, is a new supergene mineral species from the Gold Quarry mine, near
Carlin, Eureka County, Nevada, U.S.A. Nevadaite forms radiating clusters to 1 mm of prismatic crystals, locally covering surfaces
more that 2 cm across; individual crystals are elongate on [001] with a length:width ratio of >10:1 and a maximum diameter
of ~30 \'01m. It also occurs as spherules and druses associated with colorless to purple-black fluellite, colorless wavellite, strengite–
variscite, acicular maroon-to-red hewettite, and rare anatase, kazakhstanite, tinticite, leucophosphite, torbernite and tyuyamunite.
Nevadaite is pale green to turquoise blue with a pale powder-blue streak and a vitreous luster; it does not fluoresce under ultraviolet
light. It has no cleavage, a Mohs hardness of ~3, is brittle with a conchoidal fracture, and has measured and calculated
densities of 2.54 and 2.55 g/cm3, respectively. Nevadaite is biaxial negative, with \'02 1.540, \'03 1.548, \'04 1.553, 2V(obs.) = 76°,
2V(calc.) = 76°, pleochroic with X pale greenish blue, Y very pale greenish blue, Z blue, and with absorption Z >> X > Y and
orientation X = c, Y = a, Z = b. Nevadaite is orthorhombic, space group P21mn, a 12.123(2), b 18.999(2), c 4.961(1) Å , V
1142.8(2) Å 3, Z = 1, a:b:c = 0.6391:1:0.2611. The strongest seven lines in the X-ray powder-diffraction pattern [d in Å(I)(hkl)]
are: 6.077(10)(200), 5.618(9)(130), 9.535(8)(020), 2.983(6)(241), 3.430(4)(041), 2.661(4)(061), and 1.844(4)(352). A chemical
analysis with an electron microprobe gave P2O5 32.54, Al2O3 27.07, V2O3 4.24, Fe2O3 0.07, CuO 9.24, ZnO 0.11, F 9.22, H2O
(calc.) 23.48, OH ? F –3.88, sum 102.09 wt.%; the valence states of V and Fe, and the amount of H2O, were determined by
crystal-structure analysis. The resulting empirical formula on the basis of 63.65 anions (including 21.65 H2O pfu) is (Cu2+
Zn0.02 V3+
0.98 Fe3+
0.01 Al1.15)\'054.16 Al8 P7.90 O32 [F8.37 (OH)1.63]\'0510 (H2O)21.65. The crystal structure of nevadaite was solved by
direct methods and refined to an R index of 4.0% based on 1307 observed reflections collected on a four-circle diffractometer
with MoK\'02 X-radiation. The structure consists of ordered layers of vertex-sharing octahedra and tetrahedra alternating with
layers of disordered vertex-sharing and face-sharing octahedra in the b direction. [Al\'065] chains of octahedra are decorated by
(PO4) tetrahedra that share vertices with octahedra adjacent in the chain. These chains link in the c direction by sharing vertices
between octahedra and tetrahedra to form an ordered layer of the form [Al8(PO4)8F8(H2O)8]. In the disordered layer, octahedra containing positionally disordered Cu2+, V3+, Al and \'01 (vacancy) share trans faces to form columns that link by sharing octahedron
vertices to form ribbons extending in the c direction; the resulting layer has the form {(Cu2+
2\'012V3+,Al)\'056 (H2O)12 (OH)2
(H2O)x}, x ? 2. The layers link in the b direction by sharing vertices between octahedra and tetrahedra. Although decorated chains
topologically equivalent to that in nevadaite are common in many oxysalt minerals, its chain is geometrically distinct from those
topologically equivalent chains. The M–M linkage along the [M\'065] chains in most minerals take place through trans vertices of
the octahedra, with one example of linkage through cis vertices; in nevadaite, the M–M linkage involves both trans and cis
vertices, as does the chain in slavíkite. In most of these decorated chains, alternate tetrahedra along the chain occur either in a
trans or a cis arrangement. In nevadaite and slavíkite, the tetrahedra are arranged in both trans and cis arrangements; the arrangements
in these two minerals are geometrically distinct, however.