Joosteite, Mn2+(Mn3+, Fe3+)(PO4)O: a new phosphate mineral from the Helikon II Mine, Karibib, Namibia
Keller, Paul; Fontan, François; Roldan, Francisco Velasco; de Parseval, Philippe
published: Feb 28, 2007
ArtNo. ESP154018302006, Price: 29.00 €
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, Dcalc = 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(P0.98O4)O. The name of the new mineral honours Mrs. Charlotte Jooste, Karibib, Namibia.