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Published January 2015 | metadata_only
Journal Article

Esquireite, BaSi_6O_(13)·7H_2O, a New Layer Silicate from the Barium Silicate Deposits of California


Esquireite, BaSi_6O_(13)·7H_2O, is a new mineral from the Esquire #1 claim along Rush Creek, eastern Fresno County, California, USA, and a Ba-silicate lens on the NW slope of Trumbull Peak, Mariposa County, California, USA. Esquireite is a low-temperature hydrothermal alteration product of sanbornite and is found on surfaces of sanbornite. The mineral occurs as colorless rectangular blades, elongated and striated parallel to [010] and flattened on {001}. The streak is white, the luster is vitreous to pearly, and the crystals are transparent. The Mohs hardness is about 2. The tenacity is somewhat flexible, but not elastic, with brittle failure. The fracture is irregular and there are two cleavages: perfect on {001} and fair on {100}. The measured and calculated densities are 2.18(2) g/cm^3 and 2.237 g/cm^3, respectively. Esquireite is biaxial (+), with α 1.477(1), β 1.481(1), γ 1.492 (calc.) (white light); 2V_(meas) = 63.8(6)°; no dispersion or pleochroism; optical orientation: Y = b; Z ^ c ≈ 22° in obtuse β. Six electron-microprobe analyses gave the following empirical formula, based on 20 O apfu: Ba_(0.95)Si_(6.00)O_(20)H_(14.10). Esquireite is monoclinic, space group C2, with cell parameters a 13.601(4), b 4.9222(10), c 15.092(5) Å, β 111.578(19)°, V 939.6(4) Å^3, and Z = 2. The eight strongest lines in the X-ray powder diffraction patterns are [d_(obs) Å(I)(hkl)]: 7.02(38)(002), 5.11(33)(201), 4.649(66)(003,203), 4.191(100)(111), 3.339(65)(402,311,312), 2.967(32)(205,114,311), 2.343(33)(multiple), and 2.261(35)(multiple). The crystal structure (R_1 = 10.8% for 323 reflections with F_o > 4σ F) contains four-tetrahedra-thick [Si_6O_(13)]^(2–) silicate layers with Ba(H_2O)_8^(2+) polyhedra between the layers.

Additional Information

© 2015 Mineralogical Association of Canada. Received October 15, 2014, revised manuscript accepted January 22, 2015. Associate Editor James Evans, reviewer Frank Hawthorne, and an anonymous reviewer are thanked for their constructive comments on the manuscript. The Caltech EMP analyses were supported by a grant 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.

Additional details

August 20, 2023
August 20, 2023