Wayneburnhamite, Pb9Ca6(Si2O7)3(SiO4)3, an apatite polysome; the Mn-free analog of ganomalite from Crestmore, California

• Published in: The American mineralogist Vol. 101; no. 11; pp. 2423 - 2429
• Main Authors: Kampf, Anthony R, Housley, Robert M, Rossman, George R
• Format: Journal Article
• Language: English
• Published: Washington Mineralogical Society of America 01.11.2016; Walter de Gruyter GmbH
• Subjects: apatite; apatite polysome; California; chain silicates; chemical composition; Crestmore; Crestmore California; crystal chemistry; crystal form; Crystal structure; Crystals; formula; FTIR spectra; ganomalite; hardness; infrared spectra; Jacobsberg Mine; lead; lone-electron pairs; metals; Mineralogy; new mineral; new minerals; optical properties; orthosilicates; phosphates; polysomes; Raman spectra; Riverside County California; silicates; sorosilicates; space groups; spectra; spectroscopy; Spectrum analysis; United States; valency; vesuvianite; Wayneburnhamite; wollastonite; wollastonite group; X-ray diffraction data
• ISSN: 0003-004X; 1945-3027
• DOI: 10.2138/am-2016-5844

Wayneburnhamite (IMA2015-124), Pb9Ca6(Si2O7)3(SiO4)3, is a new mineral from the Commercial quarry, Crestmore, Riverside County, California, where it occurs as a metasomatic mineral on fracture surfaces in vesuvianite/wollastonite rock. Wayneburnhamite crystals are sky-blue hexagonal tablets and prisms up to 0.5 mm in maximum dimension. The streak is white. Crystals are transparent to translucent with vitreous to resinous luster. The Mohs hardness is 31/2, the tenacity is brittle, the fracture is conchoidal, and there is no cleavage. The calculated density is 5.271 g/cm3 The mineral is optically uniaxial (+), with w = 1.855(5), and e = 1.875(5) (white light). The pleochroism is E sky blue and O lighter sky blue; E > O weak. Raman and infrared spectra are consistent with the crystal structure, but suggest a very minor hydrous component. The empirical formula (based on 9 Si apfu) is (Pb8.33Sr0.04[]0.63)Σ9.00(Ca5.40Cu0.272+[]0.33)Σ6.0 0Si9S0.21O32.64Cl0.05. Wayneburnhamite is hexagonal, P6, a = 9.8953(9), c = 10.2054(7) A, V = 865.40(17) A3, and Z = 1. The eight strongest lines in the X-ray powder diffraction pattern are [dobs in A(I)(hkl)]: 4.95(52)(110); 4.45(64)(111); 3.550(77)(112); 3.232(54)(120); 3.086(100)(121); 2.847(60)(300); 2.798(48)(113); and 2.734(83)(212). The structure determination (R1 = 3.01% for 1063 Fo > 4σF) shows wayneburnhamite to be an apatite polysome isostructural with ganomalite, differing only in that the site occupied dominantly by Mn in the structure of ganomalite is occupied dominantly by Ca in the structure of wayneburnhamite. The structure refinement of wayneburnhamite appears to represent a rare case in which the approximate locations of the Pb2+ 6s2 lone-electron pairs can be seen as electron density residuals.