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Santo Domingo, Dominican Republic

Mcdonald A.M.,Laurentian University | Proenza J.A.,University of Barcelona | Zaccarini F.,University of Leoben | Rudashevsky N.S.,Center for New Technologies | And 7 more authors.
European Journal of Mineralogy | Year: 2010

Garutiite (Ni,Fe,Ir) is a new hexagonal polymorph of native Ni discovered in chromitite from Loma Peguera, Dominican Republic. The mineral was identified in heavy mineral concentrates obtained through the use of electric pulse disaggregation (EPD) and hydroseparation (HS) techniques. It forms as anhedral, botryoidal grains typically 10-60 mm in size (maximum of 110 mm). Grains are single or composite, frequently porous and zoned, and occasionally display an unusual lamellar internal texture. Associated minerals include hexaferrum, ferrian chromite, chlorite-group minerals, serpentine-group minerals, awaruite, irarsite, laurite, native Ru and unidentified species including Ru-Os-Ir-Fe and Pt-Ni-Fe-Ir compounds, Pt(Ni,Fe)3, (Fe,Ru,Ni,Os,Ir,Co)2S and RhNiAs. The mineral is megascopically grey to grey-black with a metallic luster. In plane-polarized light, garutiite is white in color, exhibits a very weak anisotropy, and no pleochroism, bireflectance or internal reflections were observed. No cleavage was noted and the hardness could not be determined owing to the porous nature of the mineral. The calculated density is 11.33 (1) g/cm3. Reflectance values (%) in air are: 63.8 at 470, 65.9 at 546, 67.0 at 589 and 68.0 at 650 nm. The average result of electron microprobe analyses (n = 42 from 27 grains) is: Ni 27.91, Fe 19.94, Ir 43.78, Pt 6.98, Co 0.55, Cu 0.43, Ru, 0.50, Rh 0.74, Os 0.67, total 101.51 wt%, corresponding to (Ni0.421Fe0.316Ir0.202Pt0.032Co 0.008Cu0.006Rh0.006Ru0.004Os 0.003)σ1 or the simplified formula, (Ni,Fe,Ir). Garutiite is the Ni analogue of hexaferrum, osmium and ruthenium and is classified as belonging to the osmium group. As such, the mineral is considered to be hexagonal, crystallizing in space group P63/mmc with a 2.6941(4) and c 4.2731(6) Å , V = 26.86(1) Å 3, Z = 2. The strongest lines of the X-ray powder diffraction pattern [d(in Å )(I)(hkl)] are: 2.330(50)(100), 2.136(30)(002), 2.046(100)(101), 1.576(30)(102), 1.3470(40)(110), 1.2155(40)(103). Based on its morphology, internal texture, and the associated minerals, garutiite is interpreted to be secondary in origin, i.e., having formed at low temperatures during post magmatic processes, such as serpentinization and/or lateritization. The name honors Prof. Giorgio Garuti, in recognition of his contributions to the understanding of the mineralogy of platinum-group elements. © 2010 E. Schweizerbart'sche Verlagsbuchhandlung. Source


Vymazalova A.,Czech Geological Survey | Laufek F.,Czech Geological Survey | Drabek M.,Czech Geological Survey | Stanley C.J.,Natural History Museum in London | And 6 more authors.
Canadian Mineralogist | Year: 2012

Zaccariniite, RhNiAs, is a new platinum-group mineral discovered in the Loma Peguera ophiolitic chromitite, Dominican Republic. The mineral forms anhedral grains (1-20 μm in size) and occurs intergrown with garutiite, in association with hexaferrum, Ru-Os-Ir-Fe alloys, Ru-Os-Ir-Fe oxygenated compounds, and chromite. Zaccariniite is opaque and has a metallic luster and a grey streak. The mineral is brittle, with no cleavage. Values of VHN5 (10 indentations on different grains of synthetic RhNiAs) fall between 166 and 286 kg/mm2, with a mean value of 218 kg/mm2, corresponding to a Mohs hardness of approximately 3.5-4. Under plane-polarized reflected light, the mineral is white with brownish to pinkish tints, has moderate to strong bireflectance, a strong white to pinkish brownish white pleochroism, and strong anisotropy, with rotation tints from orange to blue-green; it exhibits no internal reflections. Reflectance values of zaccariniite in air (R1, R2 in %) are: 49.4, 49.4 at 470 nm; 52.4, 53.2 at 546 nm; 54.2, 53.2 at 589 nm; and 56.6, 53.3 at 650 nm. Three electron microprobe analyses of natural zaccariniite gave an average composition of: Rh 41.77, Os 0.51, Ir 0.64, Ru 0.46, Pd 0.34, Ni 23.75, Fe 0.53, As 27.84, S 0.10, for a total of 96.09 wt.%, corresponding to the empirical formula (Rh1.01Os0.01Ir 0.01Ru0.01Pd0.01)Σ1.05(Ni 1.00Fe0.02)Σ1.02(As0.92S 0.01)Σ0.93 based on three atoms. The average result of twenty-eight analyses of synthetic zaccariniite is: Rh 44.57, Ni 24.50, and As 31.82 total 100.88 wt.%, corresponding to Rh1.02Ni 0.98As1.00. The mineral is tetragonal, belongs to space group P4/nmm with lattice parameters a = 3.5498(1), c = 6.1573(2) Å, V = 77.59(1) Å3, Z = 2, and crystallizes with the Cu2Sb structure type. The strongest lines in the X-ray powder-diffraction pattern of synthetic zaccariniite [d in Å(I)(hkl)] are: 2.5092(40)(110), 2.3252(100)(111,102), 1.9453(51)(112), 1.7758(80)(103,200), 1.2555(40)(213,220), 1.1044(22)(302,311), 1.0547(23)(312), 0.9730(42)(215). The new Rh-Ni arsenide is named after Federica Zaccarini in recognition of her important contributions to the mineralogy of platinum-group elements. Source


Tauler E.,University of Barcelona | Proenza J.A.,University of Barcelona | Gali S.,University of Barcelona | Lewis J.F.,George Washington University | And 5 more authors.
Clay Minerals | Year: 2010

New chemical and structural data on sepiolite-falcondoite in garnierite veins from the Falcondo Ni-laterite deposits, central Dominican Republic, are reported. Samples of Ni-sepiolite-falcondoite vary in colour from whitish green to green depending on the NiO content (wt.%) and the amount of silica present. The texture is normally schistose and friable but samples with considerable quartz and/or amorphous silica are compact and hard. Back-scattered electron images indicate that the samples are composed of at least three generations of Ni-sepiolite-falcondoite. The extreme refined cell parameters for Ni-sepiolite-falcondoite vary from 13.400(2), 27.006(4), 5.273(1) Å to 13.340(3), 27.001(6), 5.267(1) Å (space group Pncn). As the Ni content increases there is a small reduction in the a parameter. Chemical compositions determined by electron probe microanalysis cover a large interval of the Ni-sepiolite-falcondoite solid solution (Fal3 and Fal77). Individual samples show a considerable range in composition with the widest range determined in one sample from 4.63 to 22.40 wt.% NiO. © 2010 Mineralogical Society. Source

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