Melanotekite, an orthorhombic, Pb-Fe-sorosilicate;Pb2Fe2[O2|Si2O7], is found associating with willemite(trigonal, nesosilicate;Zn2SiO4) from a quarry at Numata City, Gunma prefecture. Melanotekite occurs as a wedge-shaped crystal or radial aggregates of needles up to 2mm in length in a cavity or in a fissure of host rocks in alteration zone of gabbro. Associating minerals are mainly willemite and quartz. Chemical analyses of melanotekite by EDS show that the atomic ratio of Pb:Fe:Si is nealy equal to 1:1:1 which are compatible with the ideal composition. On melanotekite, principle lines of reflection obtained by a X-ray powder diffraction method (d/I) are, 5.50(75), 5.02(18), 2.94(20), 2.91(45), 2.86(18), 2.73(100), 2.41(30), 1.695(88), 1.609(66), 1.467(17) and lead to lattice parameters; a=6.978, b=10.99, c=10.02(Å). Willemite, containing a small amount of manganese, produces fluorescence and phosphorescence under short-wave UV.
