Joosteite, Mn²⁺(Mn³⁺, Fe³⁺)(PO₄)O: a new phosphate mineral from the Helikon II Mine, Karibib, Namibia

Authors: Keller, Paul; Fontan, François; Roldan, Francisco Velasco; de Parseval, Philippe

Source: Neues Jahrbuch für Mineralogie - Abhandlungen, Volume 183, Number 2, February 2007 , pp. 197-201(5)

Publisher: E. Schweizerbart'sche Verlagsbuchhandlung

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Abstract:

Joosteite, Mn²⁺ (Mn³⁺, Fe³⁺)(PO₄)O, is a new mineral species that was found in the granitic rare element pegmatite Helikon II, Karibib, Namibia. The new mineral is the Mn³⁺-analogue of staněkite-Mabc, (Mn, Fe, Mg)²⁺Fe³⁺ (PO₄)O. The associated minerals are: lithiophilite, sicklerite, eosphorite, amblygonite, varulite, dickinsonite, hureaulite, apatite and unidentified Fe/Mn oxides. The new mineral has been formed by alteration processes at the expense of pegmatitic lithiophilite.

Joosteite exhibits a black lustre and occurs as irregular small aggregates up to 3 mm in length. It is opaque to dark brown in thin sections and displays grey colour with a brownish tinge, low to moderate bireflection, distinct anisotropy and no internal reflections. Joosteite is monoclinic, space group I2/a, a 11.888(2), b 6.409(1), c 9.804(2) Å, β 106.17(3)°, V = 717.3(3) Å³, Z = 8, D_calc = 4.13 g/cm³. Strongest lines of the X-ray powder diffraction pattern [d (I) hkl] are 2.819 (10) 013/−402, 3.077 (8) -121, 3.209 (6) 202/020, 2.082 (5) 031, 1.787 (5) −523/512, 1.495 (5) −721. Electron microprobe analysis revealed the following chemical composition (in wt.%): Na₂O 0.22, MgO 0.43, Al₂O₃ 0.03, P₂O₅ 29.97, K₂O 0.15, CaO 0.02, MnO 31.14, Mn₂O₃ 22.80 and Fe₂O₃ 12.86, sum = 97.62. The simplified empirical formula based on five O atoms is: (Mn²⁺_1.00Mn³⁺_0.64Fe³⁺_0.36)_∑2.00(P_0.98O₄)O. The name of the new mineral honours Mrs. Charlotte Jooste, Karibib, Namibia.

Keywords: JOOSTEITE; MN2+(MN3+, FE3+)(PO4)O; NEW PHOSPHATE MINERAL; STANEKITE; GRANITIC PEGMATITES; HELIKON II MINE; KARIBIB; NAMIBIA

Document Type: Research article

DOI: http://dx.doi.org/10.1127/0077-7757/2007/0069

Publication date: 2007-02-01

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