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Published August 2009 | Supplemental Material + Published
Journal Article Open

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

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Abstract

The new mineral plumbophyllite, Pb2Si4O10·H2O, orthorhombic with space group Pbcn and cell parameters a = 13.2083(4), b = 9.7832(3), c = 8.6545(2) Å, V = 1118.33(5) Å^3, and 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, sepiolite, 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/cm^3 and the calculated density is 3.940 g/cm^3. Optical properties (589 nm): biaxial (+), {alpha} = 1.674(2), β = 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, SiO_2 36.22 wt%, and CHN analysis provided H_2O 3.29 wt% for a total of 99.99 wt%. Powder IR spectroscopy confirmed the presence of H_2O and single-crystal IR spectroscopy indicated the H_2O to be oriented perpendicular to the b 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, and 2.243(521/332)50. The atomic structure (R1 = 2.04%) consists of undulating sheets of silicate tetrahedra between which are located Pb atoms and channels containing H_2O (and Pb^(2+) lone-pair electrons). The silicate sheets can be described as consisting of zigzag pyroxene-like (SiO_3)_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.

Additional Information

© 2009 Mineralogical Society of America. Manuscript received November 24, 2008. Manuscript accepted March 30, 2009. Joe Marty and Brent Thorne are thanked for providing the specimens of plumbophyllite used in this study. The IR and Raman spectroscopy as well as the microprobe analyses were supported by a grant to Caltech from the Northern California Mineralogical Association. The remainder of this study was funded by the John Jago Trelawney Endowment to the Mineral Sciences Department of the Natural History Museum of Los Angeles County. Stephen J. Guggenheim and Sergey Krivovichev provided helpful comments on the structure. Deposit item AM-09-036, observed and calculated structure amplitudes and CIF.

Attached Files

Published - Kampf2009p5842Am_Mineral.pdf

Supplemental Material - Kampf_p1198_09.doc

Supplemental Material - plumbophyllite.cif

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Created:
August 22, 2023
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October 19, 2023