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Semi-precious stones
Published in Francis P. Gudyanga, Minerals in Africa, 2020
Pyrope Mg3Al2(SiO4)3 has a colour that varies from deep red to black. The magnesium can be replaced by calcium and ferrous ions. As a mineral it is essentially an isomorphous mixture of pyrope and almandine in proportion 2:1. It is an indicator mineral for high-pressure rocks and is often contained in mantle-derived rocks, peridotites and eclogites.
Microhardness-compositional relationship of Fe3O4-Mn3O4 series spinels from ferromanganese sinter and its relationship to sinter strength
Published in Mineral Processing and Extractive Metallurgy, 2023
M. J. Peterson, S. Hapugoda, J. R. Manuel
The micro-probe was operated with an accelerating voltage of 15 kV, a probe current of 15 nA, and a spot size of 5 to 1 μm, X-Ray counting time was 60 s on standards, 30 s for major elements, 40 s for minor elements and 5–10 s on background. The instrument was calibrated with mineral, oxide and metal standards selected from the Taylor-standard set and Geology-standard set reference standards (Taylor and Kuyatt 1994). The main standards selected and the corresponding elements were as follows: Kakanui pyrope garnet – Mg, wollastonite – Ca and Si, chalcopyrite – Cu and S, galena – Pb, kyanite – Al, hematite – Fe and O, apatite – P, spessartine – Mn, MgO – Mg, rutile – Ti. After setting up the five spectrometers to analyse the separate elements the X-ray counts were measured on each standard and the standards were later analysed as unknown material to compare the certified values for the standards.
Physico-chemical characterization of detrital sillimanite and garnet: Insights into REE elements, crystal structure and morphology
Published in Marine Georesources & Geotechnology, 2022
Rajan Girija Rejith, Mayappan Sundararajan, Sreekantaiyer Ramaswamy, Abdul Azeez Peer Mohamed, Manavalan Satyanarayanan
Garnet present in the study area belongs to the almandine of the pyralspite group having the chemical formula of Fe3Al2Si3O12 (Deer, Howie, and Zussman 1982). The Raman peaks measured for the present sample indicate the almandine group, not any other silicate garnets such pyrope, spessartine, etc. Theoretically, the modes of vibrations are represented as Γ = 3 A1g+5A2g+8Eg+14F1g+14F2g+5A1u+5A2u +10Eu+17F1u+16F2u with 25 Raman active modes such as A1g, Eg, and F2g and 17 infrared active modes like F1u. The symmetry and mode assignments for the Raman spectra of garnet are given in Figure 2(b) and Table 2. The SiO4 tetrahedra of garnet structure cause the active Raman peaks at 351 (rotational vibration), 522 (internal bending), and 921 cm−1(stretching vibrations) (Kolesov and Geiger 1998). The R(SiO4)4- vibrations belong to an entire tetrahedral unit whereas the T(SiO4)4- vibrations are caused by oxygen anions. Thus, low frequencies are seen for T(SiO4)4 modes compared to R(SiO4)4-. The low frequencies measured in the range of 170 to 280 cm−1 can be assigned to F2g, while the weak peak Eg at ∼255 cm−1 is due to X 2+(x, y) and X 2+(z)-translations.
An updated catalogue of New Zealand’s mantle peridotite and serpentinite
Published in New Zealand Journal of Geology and Geophysics, 2020
Orthopyroxene and clinopyroxene trace elements from both Chatham Island locations indicate the peridotites have been metasomatised, probably by carbonatitic magmas (McCoy-West et al. 2015; Scott et al. 2016b). Clinopyroxene and bulk rock peridotite analyses have unradiogenic 87Sr/86Sri (0.70283–0.70304), and radiogenic 143Nd/144Ndi (0.51275–0.51279) and 206Pb/204Pbi (19.5–20.8), 207Pb/204Pbi (15.7) and 208Pb/206Pbi (c. 38.8–39.9) (McCoy-West et al. 2016). While the Sr and Nd isotopes are typical of New Zealand mantle rocks, the Pb isotopes extend to some of the most radiogenic compositions (McCoy-West et al. 2016); these may be associated with lithosphere from under the adjacent Hikurangi Plateau (Figure 1B). The 3He/4He values obtained from one sample are very low (1.5; Hoke et al. 2000). Water measurements indicate that the peridotites are anhydrous (Li et al. 2018). Cr-free pyrope garnet occurs on the northern beaches of the main Chatham Island and may be a megacrystic component to some basalts (Scott 2013).