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Roymillerite, Pb24Mg9(Si9AlO28)(SiO4)(BO3)(CO3)10(OH)14O4, a new mineral: mineralogical characterization and crystal chemistry
Russian Acad Sci, Inst Problems Chem Phys, Chernogolovka 142432, Moscow Region, Russia..
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Geol Survey Sweden, Dept Mineral Resources, Box 670, S-75128 Uppsala, Sweden.
Russian Acad Sci, Inst Crystallog, 59 Leninskiy Prospekt, Moscow 117333, Russia.;St Petersburg State Univ, Dept Crystallog, Univ Skaya Nab 7-9, St Petersburg 199034, Russia.;Russian Acad Sci, Nesmeyanov Inst Organoelement Cpds, GSP-1,Vavilova St 28,V-334, Moscow 119991, Russia..
St Petersburg State Univ, Dept Crystallog, Univ Skaya Nab 7-9, St Petersburg 199034, Russia..
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2017 (English)In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 44, no 10, p. 685-699Article in journal (Refereed) Published
Abstract [en]

The new mineral roymillerite Pb24Mg9(Si9AlO28)(SiO4)(BO3)(CO3)(10)(OH)(14)O-4, related to britvinite and molybdophyllite, was discovered in a Pb-rich assemblage from the Kombat Mine, Grootfontein district, Otjozondjupa region, Namibia, which includes also jacobsite, cerussite, hausmannite, sahlinite, rhodochrosite, barite, grootfonteinite, Mn-Fe oxides, and melanotekite. Roymillerite forms platy single-crystal grains up to 1.5 mm across and up to 0.3 mm thick. The new mineral is transparent, colorless to light pink, with a strong vitreous lustre. Cleavage is perfect on (001). Density calculated using the empirical formula is equal to 5.973 g/cm(3). Roymillerite is optically biaxial, negative, alpha = 1.86(1), beta ae gamma = 1.94(1), 2V (meas.) = 5(5)A degrees. The IR spectrum shows the presence of britvinite-type tetrahedral sheets, , , and OH- groups. The chemical composition is (wt%; electron microprobe, H2O and CO2 determined by gas chromatography, the content of B2O3 derived from structural data): MgO 4.93, MnO 1.24, FeO 0.95, PbO 75.38, B2O3 0.50, Al2O3 0.74, CO2 5.83, SiO2 7.90, H2O 1.8, total 99.27. The empirical formula based on 83 O atoms pfu (i.e. Z = 1) is Pb24.12Mg8.74Mn1.25Fe0.94B1.03Al1.04C9.46Si9.39H14.27O83. The crystal structure was determined using single-crystal X-ray diffraction data. The new mineral is triclinic, space group P , with a = 9.315(1), b = 9.316(1), c = 26.463(4) , alpha = 83.295(3)A degrees, beta = 83.308(3)A degrees, gamma = 60.023(2)A degrees, V = 1971.2(6) (3). The crystal structure of roymillerite is based built by alternating pyrophyllite-type TOT-modules Mg-9(OH)(8)[(Si,Al)(10)O-28] and I-blocks Pb-24(OH)(6)O-4(CO3)(10)(BO3,SiO4). The strongest lines of the powder X-ray diffraction pattern [d, (I, %) (hkl)] are: 25.9 (100) (001), 13.1 (11) (002), 3.480 (12) (017, 107, -115, 1-15), 3.378 (14) (126, 216), 3.282 (16) (-2-15, -1-25), 3.185 (12) (-116, 1-16), 2.684 (16) (031, 301, 030, 300, 332, -109, 0-19, 1-18), 2.382 (11) (0.0.-11). Roymillerite is named to honor Dr. Roy McG. Miller for his important contributions to the knowledge of the geology of Namibia.

Place, publisher, year, edition, pages
2017. Vol. 44, no 10, p. 685-699
Keywords [en]
New mineral, Roymillerite, Britvinite, Crystal structure, IR spectroscopy, Kombat Mine, Namibia
National Category
Geology
Identifiers
URN: urn:nbn:se:uu:diva-340914DOI: 10.1007/s00269-017-0893-2ISI: 000414161200001OAI: oai:DiVA.org:uu-340914DiVA, id: diva2:1180369
Available from: 2018-02-05 Created: 2018-02-05 Last updated: 2018-02-23Bibliographically approved

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