CHLADNIITE, NA2CAMG7(PO4)6 - A NEW MINERAL FROM THE CARLTON (IIICD) IRON METEORITE

A new mineral, chladniite, Na2CaMg7(PO4)6, occurs as a single grain wi thin a silicate-bearing inclusion in the Carlton (IIICD) iron meteorit e. It is hexagonal, R3BAR, a = 14.967, c = 42.595 angstrom. It is name d for E.F.F. Chladni (1756-1827), who is widely regarded as the founde r of the science of meteoritics. Chladniite is colorless and transpare nt when powdered. In polished section, the mineral is gray, dark, weak ly bireflecting, and weakly anisotropic. Cleavage, rarely visible, is rhomboidal in plan. Polishing hardness is less than low-calcium orthop yroxene, but greater than Fe,Ni metal. Reflectance measurements at 589 nm give R1 = 5.3%, R2 = 5.6%. Assuming an absorption coefficient k = 0, the calculated refractive indices are n1 = 1.60, n2 = 1.62. Stronge r reflections on Gandolfi X-ray film of chladniite are d = 3.694 (0,1, 11; 306) s, 3.5 58 (0,2,10;0,0,12) m, 2.960 (0,1,14) s, 2.753 (1,3,10) s, 2.500 (3,3,0) m, 2.126 (2,4,10; 2,3,14; 0,2,19) m, and 1.851 (701; 1,5,14; 6,0,12) m. Microprobe analysis gives, in weight percent, Na2O 6.57, CaO 6.59, MgO 33.5, FeO 2.23, MnO 0.30, SiO2 0.59, P2O5 49.9, to tal 99.68, leading to the empirical formula Na1.77Ca0.98Si0.08(Mg6.96F e0.26Mn0.04)SIGMA = 7.26(P0.98O4)6. Chladniite is the Mg analogue of f illowite and johnsomervilleite, which are Mn- and Fe-dominated end-mem bers, respectively. Chladniite occurs with chlorapatite, olivine, orth opyroxene, plagioclase, schreibersite, Fe,Ni metal, and troilite.