Kobokoboite, Al6(PO4)4(OH)6 • 11H2O, a new mineral from the Kobokobo pegmatite, Democratic Republic of the Congo

Kobokoboite, ideally Al-6(PO4)(4)(OH)(6)center dot 11H(2)O, is a new mineral (IMA2009- 057), from the Kobokobo pegmatite, South Kivu Province, Democratic Republic of the Congo. Kobokoboite forms 0.1 to 0.15- mm thick crusts and coatings of pearly white, glistening, platy crystals, usually on a matrix of frondelite and keckite. Other associated minerals reported include a fine- grained mixture of planerite, variscite and wavellite ("coeruleolactite''), as well as muscovite- 2M2, evansite and apatite-(CaOH). Individual crystals of kobokoboite are rectangular plates or flattened blades on (001). The dominant form observed is {001}. The crystals have a pearly lustre, are translucent but transparent on edge, have a white streak and are non- fluorescent. Mohs hardness is about 2 (estimated). The fracture is irregular and the tenacity is brittle. Measured density is 2.21(3); calculated density is 2.287 g cm(-3). Kobokoboite crystals are biaxial (-), with the indices of refraction beta = 1.558(2) and gamma = 1.562(2) measured in white light and with 2V(meas). 60-80 degrees. Orientation: X approximate to c; Y and Z could not be determined. Crystals are non-pleochroic. The empirical formula (based on (O + OH + F) = 33) is: (Al5.85Fe0.143+Ca0.03Na0.02)(Sigma 6.04)(PO4)(3.97)[(OH)(5.80)F-0.34] (Sigma 6.14) . 10.98H(2)O. Kobokoboite is triclinic, space group P-1 or P (1) over bar , a = 7.460(1), b = 7.737(1), c = 12.385(5) A, alpha = 102.79(2), beta = 90.20(3), gamma = 116.33(2)degrees, V = 620.6(3) angstrom(3) nd Z = 1. The five strongest lines in the powder X- ray diffraction pattern are [ dobs inA, (I)]: 11.990, (100); 6.868, (45); 3.552, (39); 6.006, (33); 3.081, (29). The chemistry and cell parameters of kobokoboite suggest a structural relationship with planerite and the new mineral IMA2005- 025a, where the same sheet of octahedra and tetrahedra parallel to {001} are responsible for a, b and gamma. The name is in reference to the type locality.