Kobokoboite, Al (sub 6) (PO (sub 4) ) (sub 4) (OH) (sub 6) .11H (sub 2) O, a new mineral from the Kobokobo Pegmatite, Democratic Republic of the Congo

Kobokoboite, ideally Al (sub 6) (PO (sub 4) ) (sub 4) (OH) (sub 6) .11H (sub 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-2M (sub 2) , 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 (super -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 (sub meas.) =60-80 degrees . Orientation: X nearly equal c; Y and Z could not be determined. Crystals are non-pleochroic. The empirical formula (based on (O+OH+F)=33) is: (Al (sub 5.85) Fe (super 3+) (sub 0.14) Ca (sub 0.03) Na (sub 0.02) ) (sub Sigma 6.04) (PO (sub 4) ) (sub 3.97) [(OH) (sub 5.80) F (sub 0.34) ] (sub Sigma 6.14) .10.98H (sub 2) O. Kobokoboite is triclinic, space group P1 or P1, a=7.460(1), b=7.737(1), c=12.385(5) Aa, alpha =102.79(2), beta =90.20(3), gamma =116.33(2) degrees , V=620.6(3) Aa (super 3) and Z=1. The five strongest lines in the powder X-ray diffraction pattern are [d (sub obs) in Aa, (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.