| Reference Type | Journal (article/letter/editorial) |
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| Title | Hydroxycalciomicrolite, Ca1.5Ta2O6(OH), a new member of the microlite group from Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil |
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| Journal | Mineralogical Magazine |
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| Authors | Andrade, M. B. | Author |
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| Yang, H. | Author |
| Atencio, D. | Author |
| Downs, R. T. | Author |
| Chukanov, N. V. | Author |
| Lemée-Cailleau, M. H. | Author |
| Persiano, A. I. C. | Author |
| Goeta, A. E. | Author |
| Ellena, J. | Author |
| Year | 2017 (June) | Volume | 81 |
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| Page(s) | 555-564 | Issue | 3 |
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| Publisher | Mineralogical Society |
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| Download URL | https://rruff.info/rruff_1.0/uploads/MM81_555.pdf+ |
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| DOI | doi:10.1180/minmag.2016.080.116Search in ResearchGate |
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| Classification | Not set | LoC | Not set |
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| Mindat Ref. ID | 244899 | Long-form Identifier | mindat:1:5:244899:6 |
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| GUID | 87ff5dd0-cb9e-45db-951c-71a2f08f0e0c |
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| Full Reference | Andrade, M. B., Yang, H., Atencio, D., Downs, R. T., Chukanov, N. V., Lemée-Cailleau, M. H., Persiano, A. I. C., Goeta, A. E., Ellena, J. (2017) Hydroxycalciomicrolite, Ca1.5Ta2O6(OH), a new member of the microlite group from Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil. Mineralogical Magazine, 81 (3) 555-564 doi:10.1180/minmag.2016.080.116 |
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| Plain Text | Andrade, M. B., Yang, H., Atencio, D., Downs, R. T., Chukanov, N. V., Lemée-Cailleau, M. H., Persiano, A. I. C., Goeta, A. E., Ellena, J. (2017) Hydroxycalciomicrolite, Ca1.5Ta2O6(OH), a new member of the microlite group from Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil. Mineralogical Magazine, 81 (3) 555-564 doi:10.1180/minmag.2016.080.116 |
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| Abstract/Notes | Hydroxycalciomicrolite, Ca1.5Ta2O6(OH) is a new microlite-group mineral found in the Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil. It occurs as isolated octahedral and as a combination of octahedral and rhombic dodecahedral crystals, up to1.5 mm in size. The crystals are yellow and translucent, with a white streak and vitreous to resinous lustre. The mineral is brittle, with a Mohs hardness of 5–6. Cleavage is not observed and fracture is conchoidal. The calculated density is 6.176 g cm–3. Hydroxycalciomicroliteis isotropic, ncalc. = 2.010. The infrared and Raman spectra exhibit bands due to O–H stretching vibrations. The chemical composition determined from electron microprobe analysis (n = 13) is (wt.%): Na2O 0.36(8), CaO 15.64(13), SnO2 0.26(3),Nb2O5 2.82(30), Ta2O5 78.39(22), MnO 0.12(2), F 0.72(12) and H2O 1.30 (from the crystal structure data), O = F –0.30, total 99.31(32), yielding an empirical formula, (Ca1.48Na0.06Mn0.01)∑1.55(Ta1.88Nb0.11Sn0.01)∑2.00O6.00[(OH)0.76F0.20O0.04]. Hydroxycalciomicrolite is cubic, with unit-cell parameters a = 10.4205(1) Å, V = 1131.53(2) Å3 and Z = 8. It represents a pyrochlore supergroup, microlite-group mineral exhibiting P4332 symmetry, instead of Fd3m. Thereduction in symmetry is due to long-range ordering of Ca and vacancies on the A sites. This is the first example of such ordering in a natural pyrochlore, although it is known from synthetic compounds. This result is promising because it suggests that other species with P4332 or lower-symmetry space group can be discovered and characterized. |
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