Journal of Mineralogical and Petrological Sciences
Online ISSN : 1349-3825
Print ISSN : 1345-6296
ISSN-L : 1345-6296
Volume 102 , Issue 4
August
Showing 1-4 articles out of 4 articles from the selected issue
ORIGINAL ARTICLES
  • Anhuai LU, Xiang GAO, Changqiu WANG, Yongwen GAO, Desheng ZHENG, Tianh ...
    2007 Volume 102 Issue 4 Pages 217-225
    Published: 2007
    Released: September 05, 2007
    [Advance publication] Released: April 03, 2007
    JOURNALS FREE ACCESS
    The Xiangtan manganese deposit (XTM) was formerly considered a supergene oxide manganese deposit in South China. Here, we report upon a new identification of naturally outcropping cryptomelane from the XTM, rather than psilomelane and pyrolusite, as it was previously considered. Most crystals in aggregates of XTM cryptomelane are acicular, with a diameter from 20 nm to 120 nm. There are large pseudotetragonal tunnels in the cryptomelane formed by [MnO6] octahedral double chains with an aperture of 0.462 × 0.466 nm2. The importance of our find relates not only to manganese resource prospecting in South China, but also to the application of the octahedral molecular sieve of cryptomelane. On the basis of the study of some mineralogical characteristics, experiments on heavy metal cadmium adsorption have been done. The overall adsorption capacity of cryptomelane for Cd2+ with different electrolytes showed an increase with a pH rise from 3 to 11.5. This work also showed that in addition to an ion exchange with H+, the adsorption of Cd2+ might involve exchange with Mn and K cations in the cryptomelane structure. Isotherms for Cd2+ adsorption in about neutral pH solutions can be satisfactorily represented by the Langmuir expression and the theoretic maximum disposal capacity thus determined is 5.54 mg/g.
    Download PDF (1294K)
  • Naotaka TOMIOKA
    2007 Volume 102 Issue 4 Pages 226-232
    Published: 2007
    Released: September 05, 2007
    [Advance publication] Released: April 03, 2007
    JOURNALS FREE ACCESS
    The shear mechanism in the clinoenstatite (space group C2/c)-akimotoite (space group R3) transition under high-pressure can be explained by a sweeping of partial dislocations associated with cooperative cation displacements without any long-range atomic diffusion. The shortest translation vector, [001] on the (100) plane of clinoenstatite, dissociates into a 1/3[001] + 1/6[011] + 1/3[001] + 1/6[011] vector, and the first two partial dislocations bring about a hexagonal close packed oxygen sublattice in the akimotoite structure. This shear mechanism is considered to be a favorable mechanism under high differential stress, or at high-pressures and relatively low-temperatures, where any overpressure from the hypothetical equilibrium clinoenstatite-akimotoite phase boundary would be high, but atomic diffusion would be kinetically hindered. Therefore, this mechanism would occur in subducting cold slabs in the Earth's deep mantle and in shocked meteorites.
    Download PDF (1034K)
  • Masayuki OHNISHI, Isao KUSACHI, Shoichi KOBAYASHI, Junji YAMAKAWA
    2007 Volume 102 Issue 4 Pages 233-239
    Published: 2007
    Released: September 05, 2007
    [Advance publication] Released: June 08, 2007
    JOURNALS FREE ACCESS
    Schulenbergite and its Zn-dominant analogue occur in the Hirao mine, Osaka Prefecture, Japan. The minerals were found as crusts on the same gallery wall and in cracks of altered shale. The minerals occur as aggregates of hexagonal platy crystals up to 0.5 mm across and 0.05 mm thick. The schulenbergite is greenish blue to blue-green in color, and the Cu/(Cu + Zn) molar ratio varies from 0.67 to 0.42. The Zn-dominant analogue of schulenbergite is pale blue in color, and the Cu/(Cu + Zn) molar ratio varies from 0.30 to 0.21. The average unit cell parameters of schulenbergite and its Zn-dominant analogue calculated from the X-ray powder diffraction data were: a = 8.256 (2) and c = 7.207 (3) Å, and a = 8.292 (2) and c = 7.271 (4) Å, respectively. It is likely that schulenbergite and its Zn-dominant analogue from the Hirao mine were formed as secondary minerals from Cu and Zn ion-bearing solution that were derived from chalcopyrite and sphalerite in the host rock.
    Download PDF (743K)
  • Mariko NAGASHIMA, Masahide AKASAKA, Atsushi KYONO, Kuniaki MAKINO, Ko ...
    2007 Volume 102 Issue 4 Pages 240-254
    Published: 2007
    Released: September 05, 2007
    JOURNALS FREE ACCESS
    The crystal structures of chromian epidotes from the Sambagawa metamorphic rocks, central Shikoku, Japan, were refined using single-crystal data to investigate the distribution of chromium among the three independent octahedral sites. On the basis of the electron probe microanalysis of the chromian epidotes on the polished surface of thin sections, three chromian epidote grains in a thin section were selected for X-ray intensity data collection, and their Cr2O3 values were as much as 1.79, 4.99, and 4.74 wt%, respectively, which led to values of 0.113, 0.315, and 0.299 Cr apfu, respectively. Nevertheless, their Fe2O3 contents were nearly constant (8.1-8.7 wt%, 0.49-0.52 Fe apfu) and their SrO contents were not significant (1.8-3.2 wt%, 0.08-0.15 Sr apfu). The selected chromian epidote grains were picked out using a binocular optical microscope from the thin sections, and were labeled as CrEp1, CrEp2, and CrEp3, respectively. The oxidation state of chromium was found to be trivalent by the optical spectrum. 57Fe Mössbauer doublets with isomer shift of 0.28-0.53 mm/sec and quadrupole splitting of 1.77-2.24 mm/sec indicate an exclusive distribution of Fe3+ at the M3 site. The crystal structure of CrEp1 [a = 8.8815(6), b = 5.5956(5), c = 10.1532(5) Å, β = 115.159(2)], CrEp2 [a = 8.9165(4), b = 5.6226(2), c = 10.1728(5) Å, β = 115.2365(9)], and CrEp3 [a = 8.895(2), b = 5.610(1), c = 10.146(2) Å, β = 115.177(2)] were refined using 1145, 1853 and 1438 unique reflections, respectively, and the calculations converged at R factors of 5.8%, 6.6%, and 3.2%, respectively. The resulting structural formula were: [Ca]A1[Ca0.86Sr0.14]A2[Al]M1[Al]M2[Al0.43Cr3+0.09Fe3+0.48]M3Si3O12(OH) for CrEp1, [Ca]A1[Ca0.90Sr0.10]A2[Al0.86Cr3+0.14]M1[Al]M2[Al0.34Cr3+0.17Fe3+0.49]M3Si3O12(OH) for CrEp2, and [Ca]A1[Ca0.88Sr0.12]A2[Al0.90Cr3+0.10]M1[Al]M2[Al0.37Cr3+0.12Fe3+0.51]M3Si3O12(OH) for CrEp3. The selective distribution of Cr3+ at the M3 site in CrEp1, and the KD values (KD = (Cr3+/Al)M1/(Cr3+/Al)M3) of 0.35(3) for CrEp2 and 0.41(3) for CrEp3 show that the preference of Cr3+ in the octahedral sites is M3 > M1 » M2. The variations in the M1-Oi and M3-Oi distances indicate an equidimensional expansion of the M1O6 and M3O6 octahedra by the substitution of Cr3+(+ Fe3+) for Al3+.
    Download PDF (1020K)
feedback
Top