| Full text | |
| Author(s): |
Total Authors: 4
|
| Affiliation: | [1] Univ Sao Paulo, Sao Carlos Inst Phys, Dept Phys & Interdisciplinary Sci, Caixa Postal 369, BR-13560970 Sao Carlos, SP - Brazil
[2] Univ Sao Paulo, Inst Geociencias, Dept Mineral & Geotecton, Rua Lago 562, BR-05508080 Sao Paulo, SP - Brazil
[3] Univ Fed Minas Gerais, Inst Geociencias, Ave Antonio Carlos 6627, BR-31270901 Belo Horizonte, MG - Brazil
[4] Nat Hist Museum, Core Res Labs, Cromwell Rd, London SW7 5BD - England
Total Affiliations: 4
|
| Document type: | Journal article |
| Source: | MINERALOGICAL MAGAZINE; v. 82, n. 1, p. 111-120, FEB 2018. |
| Web of Science Citations: | 1 |
| Abstract | |
Melcherite (IMA2015-018), ideally Ba2Na2Mg{[}Nb6O19]center dot 6H(2)O, occurs as a vug mineral in the carbonatite of the Jacupiranga mine, Cajati county, Sao Paulo state, Brazil, associated with dolomite, calcite, magnetite, pyrrhotite, tochilinite, ` pyrochlore' and fluorapatite. This is also the type locality for zirkelite, quintinite, menezesite and pauloabibite. The mineral forms irregular, tabular crystals up to 200 mu m in maximum dimension. Melcherite is transparent and displays a vitreous lustre; it is beige with a white streak. It is nonfluorescent. The mineral displays perfect cleavage on [001]. Chemical composition varies from Ba2Na2Mg{[}Nb6O19]center dot 6H(2)O to (BaK)(NaCa) Mg{[}Nb6O19]center dot 6H(2)O. Empirical formulae for the first and the second compositions are: (Ba1.75K0.19)(Sigma 1.94)(Na1.80Ca0.19)(Sigma 1.99)(Mg0.96Mn0.02Al0.02)(Sigma 1.00)Nb6.02O19.00 center dot 6H(2)O and (Ba0.99K1.00)(Sigma 1.99)(Na1.02Ca0.96)(Sigma 1.98)(Mg0.95Mn0.05)(Sigma 1.00)Nb6.02O19.00 center dot 6H(2)O, respectively. Data for a single crystal with the second composition are: trigonal, R (3) over bar, a = 9.0117(6) angstrom, c = 23.3986(16) angstrom, V = 1645.64(19) angstrom(3) and Z = 3. Calculated density for this formula is 3.733 g/cm(3), and the calculated mean refractive index is 1.924. Melcherite is a hexaniobate that has structural layers parallel to the xy plane that stack along the c axis with simultaneous 1/3 {[}1 (1) over bar0] displacement so as to produce an R lattice. The melcherite structure is built by layers of {[}(Ba,K)(O,H2O)(9)] polyhedra and the {[}Nb6O19](8-) super-octahedron (Lindqvist anion) interconnected by {[}(Na,Ca)O-6] polyhedra. Cations of Mg2+ are bonded to six water molecules each and are not associated with Lindqvist oxygen ions. The mineral is named in honour of Geraldo Conrado Melcher (1924-2011), a pioneer in Jacupiranga carbonatite studies. (AU) | |
| FAPESP's process: | 11/22407-0 - New and rare Brazilian mineral species characterization |
| Grantee: | Daniel Atencio |
| Support Opportunities: | Regular Research Grants |
| FAPESP's process: | 13/03487-8 - Center of characterization of new mineral species: Raman spectroscopy, electron microprobe and X-ray and neutron diffraction |
| Grantee: | Marcelo Barbosa de Andrade |
| Support Opportunities: | Research Grants - Young Investigators Grants |