Plumbophyllite, 
a new species from the Blue Bell claims
near Baker, San Bernardino County, California



Anthony R. Kampf
Mineral Sciences Department, Natural History Museum of Los Angeles County
Los Angeles, CA  90007

George R. Rossman, Robert M. Housley
Division of Geological and Planetary Science
California Institute of Technology, Pasadena, CA 91125-2500, USA


Abstract

    The new mineral plumbophyllite, Pb2Si4O10ĚH2O, is orthorhombic with space group Pbcn and cell parameters a 13.2083(4), b 9.7832(3), c 8.6545(2) ┼, V 1118.33(5) ┼3, Z = 4. It occurs as colorless to pale blue prismatic crystals to 3 mm with wedge-shaped terminations at the Blue Bell claims, about 11 km west of Baker, San Bernardino County, California. It is found in narrow veins in a highly siliceous hornfels in association with cerussite, chrysocolla, fluorite, goethite, gypsum, mimetite, opal, plumbotsumite, quartz and wulfenite. The streak is white, the luster is vitreous, the Mohs hardness is about 5 and there is one perfect cleavage, {100}. The measured density is 3.96(5) g/cm3 and the calculated density is 3.940 g/cm3. Optical properties (589 nm): biaxial (+), alpha = 1.674(2), beta = 1.684(2), gamma = 1.708(2), 2V = 66(2)˚, dispersion r > v (strong); X = b, Y = c, Z = a. Electron microprobe analysis provided PbO 60.25, CuO 0.23, SiO2 36.22 wt.% and CHN analysis provided H2O 3.29 wt.% for a total of 99.99 wt.%. Powder IR spectroscopy confirmed the presence of H2O and single-crystal IR spectroscopy indicated the H2O to be oriented along the c axis. Raman spectra were also obtained. The strongest powder X-ray diffraction lines are [d(hkl)I]: 7.88(110)97, 6.63(200)35, 4.90(020)38, 3.623(202)100, 3.166(130)45, 2.938(312/411/222)57, 2.555(132/213)51, 2.243(521/332)50. The atomic structure (R1 = 2.13%) consists of undulating sheets of silicate tetrahedra between which are located Pb atoms and channels containing H2O (and Pb2+ lone-pair electrons). The silicate sheets can be described as consisting of zigzag pyroxene-like (SiO3)n chains joined laterally into sheets with the unshared tetrahedral apices in successive chains pointed alternately up and down, a configuration also found in pentagonite.


SEM image Plumbophyllite
blades
SEM image of plumbophyllite crystals (by RMH) 8 mm cluster of plumbophyllite colored by copper sprays of plumbophyllite crystals at high magnification


Raman data file