EDGARBAILEYITE THE FIRST KNOWN SILICATE OF MERCURY, FROM CALIFORNIA AND TEXAS Andrew C. Roberts' and Maurizio Bonardi Geological Survey of Canada 601 Booth Street Ottawa, Ontario, Canada KIA OE8 Richard C. Erd United States Geological Survey 345 Middlefield Road Menlo Park, California 94025 Alan J. Criddle, Christopher J. Stanley and Gordon Cressey Department of Mineralogy British Museum (Natural History) Cromwell Road London, England SW7 5BD Ross J. Angel Department of Geological Sciences and Department of Crystallography University College London Birkbeck College Gower Street Malet Street London, England WCIE 6BT London, England WCIE 7HX J. H. Gilles Laflamme CANMET 555 Booth Street Ottawa, Ontario, Canada KIA OGI ABSTRACT Edgarbaileyite, idealized as Hg;'SiP" is monoclinic, space group C2/m(12), with refined unit-cell parameters a = 11.725(4), b = 7.698(2), c = 5.967(2) A, ~ = 112.07(3t, V = 499.2(2) A3, a:b:c = 1.5231:1:0.7751, Z = 2. The strongest eight lines in the X-ray powder pattern are [d (I) (hkl)]:6.28 (20) (110); 3.160 (l00) (021); 3.027 (27) (221); 2.952 (34) (202); 2.765 (20) (002); 2.715 (63) (400); 2.321 (24) (421); 1.872 (36) (602). The mineral is rare, but rather widespread. At the Socrates mine, Sonoma County, California, it has been identified as thin crusts on fracture surfaces, as disseminated rounded to mammillary masses in small cavities, and as hollow mam- millary nodules; it is most closely associated with chalcedonic quartz, native mercury, cinnabar and montroydite in a host rock composed principally of magnesite and quartz. At the Clear Creek claim, San Benito County, California, the habit is identical to that at the Socrates mine; it is most closely associated with native mercury and montroydite 'Geological Survey of Canada contribution number 12989. Figure 1. Nodular masses of edgarbaileyite in a quartz-lined cavity. Field of view is 17 mm (Socrates mine), The Mineralogical Record, volume 21) May-June, 1990 215 in a host rock composed principally of quartz, magnesite and chal- who worked for the United States Geological Survey as a mercury cedony. Edgarbaileyite has also been identified on a museum specimen commodity specialist, and who studied and described mercury deposits from Terlingua, Brewster County, Texas, as ill-formed tabular ag- both in the U.S. and in Turkey. Two of the occurrences within the gregates and sheaves of crystals in cavities and fractures; it is most continental U. S. on which he reported were the Socrates mine (Bailey closely associated with montroydite, terlinguaite, eglestonite and na- 1946) and the deposits at Terlingua (Yates and Thompson, 1959). The tive mercury in a matrix of calcite, quartz and barite. Crystals range mineral and name have been approved by the Commission on New from cryptocrystalline and anhedral up to 0.2-mm platy crystal ag- Minerals and Mineral Names, I.M.A. The type locality is hereby gregates with dominant {100} form. Crystals are poly synthetically designated the Socrates mine for two reasons: (1) chronologically, it twinned on {100}. Edgarbaileyite is photosensitive and is varicolored; was the first verified occurrence, and (2) most of the megascopic ally freshly exposed material is lemon-yellow to orangish yellow; exposed identifiable edgarbaileyite comes from this locality. The holotype spec- surfaces range from dark olive-green to a lighter yellowish green to imen, which has been broken into two hand specimens, several mineral dark green-brown. Physical properties include: pale green streak with fragments, two polished grain mounts and two SEM stubs, is preserved a yellow tinge; vitreous (crystals) to resinous (masses) luster; trans- within the Systematic Reference Series of the National Mineral Col- lucent (crystals) to opaque (masses); non-fluorescent; VHN\OO 192 lection at the Geological Survey of Canada, Ottawa, under catalog (range 153-217); calculated Mohs' hardness 4; brittle; irregular to number NMC 65531. The hand specimen containing edgarbaileyite subconchoidal fracture; density 9.4(3) g/cm' (9.11 calc. for empirical from Terlingua, Texas, is housed within the mineral collections of the formula). The mineral is optically biaxial with all refractive indices British Museum (Natural History), London, under catalog number greater than 2; it has weak pleochroism and strong absorption. In BM 1906, 190. polished section, edgarbaileyite is weakly to strongly bireflectant and OCCURRENCE is not pleochroic. In plane-polarized light it is gray to slightly lighter Edgarbaileyite has been identified at two widely separated localities gray with pale lemon-yellow internal reflections. Measured reflectance in California and in a museum specimen labeled as originating from values for 2 grains in air and in oil are tabulated. Maximum and Texas. The localities are: the upper workings of the abandoned Socrates minimum calculated refractive indices (at 590 nm) are 2.58 and 2.10. mercury mine, Sonoma County, California (latitude 38°45'47"N, lon- Electron microprobe analyses (from the Socrates mine) yielded Hg 0 2 gitude 122°45'30"W); a small prospect pit near the long-abandoned = 89.6, Si02 = 8.6, sum = 98.2 weight %, corresponding to Clear Creek mercury mine, New Idria District, San Benito County, Hg~\x,Si2oo07' based on 0 = 7. Virtually identical results were ob- California (latitude 36°22'59"N, longitude l20045'58''W); and the Ter- tained from microprobe analyses of Terlingua material. The mineral lingua deposit, Brewster County, Texas (latitude 29°20'N, longitude is named for Dr. Edgar Herbert Bailey (1914-1983), distinguished 103°39'W). The mineral is rare, but is rather widespread at both geologist and mercury commodity specialist for the U.S. Geological occurrences in California. Its spatial distribution at Terlingua is un- Survey. known, but we assume it to be very rare. At the Socrates mine, edgarbaileyite is most closely associated with INTRODUCTION quartz, native mercury, cinnabar and montroydite in host rock prin- The new mineral species described here, edgarbaileyite, was first cipally composed of magnesite and quartz. Other minerals identified brought to the attention of one of us (RCE) by Dr. Edgar Bailey. He are chalcedonic quartz, opal and chromite. For more information had received a specimen containing an unidentified yellow mercury- regarding the mercury deposits found within Sonoma County and, bearing mineral from Leo Rosenhahn, who had originally collected specifically, the Socrates mine, the reader is referred to the report by the material at the Socrates mine, Sonoma County, California in 1963. Bailey (1946). Collectors should be advised that the Socrates mine The first X-ray powder pattern was run in March, 1968, and could has been bulldozed and that there are no remnants nor dump from not be identified with any known inorganic phase listed in the Powder which specimens may be obtained. Diffraction File. Somewhat later, in 1972, Edward H. Oyler collected At the Clear Creek locality, edgarbaileyite is closely associated with some specimens at the Clear Creek claim, San Benito County, Cal- native mercury, montroydite and minor cinnabar. The host rock is ifornia, and submitted a massive yellow-orange phase to RCE for predominantly quartz, magnesite, chalcedony with minor pecoraite, X-ray identification. Oyler's unknown was found to be identical to opal, goethite, chromite, montmorillonite, huntite, dolomite, gypsum Rosenhahn's previously unidentified mineral. However, a lack of suf- and chlorite. Mercury-bearing minerals identified by X-ray diffraction ficient pure material prevented a more detailed mineralogical study at analysis include edoylerite (Erd et al., in preparation, IMA approved), that time. In 1987, Mr. Oyler and John Parnau brought RCE some wattersite (Erd et al., in preparation, IMA approved), metacinnabar, additional specimens from the Socrates mine, which Parnau had col- eglestonite, calomel, terlinguaite, mosesite, gianellaite and five un- lected in 1963. Megascopic examination and X-ray powder diffraction named mercury-bearing phases that are currently under investigation. study confirmed the presence of the same mineral previously identified A description of the geology of the Clear Creek mercury mine is given in 1968 and in 1972. In addition, the same mineral from Terlingua, by Eckel and Myers (1946). Brewster County, Texas, was found by AJC during the acquisition of At both Californian localities, edgarbaileyite has been identified in optical reflectance and chemical data for a range of oxide minerals several different varietal forms: as thin crusts on fracture surfaces, for eventual inclusion in the QDF (The Quantitative Data File for generally coating cinnabar or quartz; as disseminated rounded to mam- Ore Minerals, Criddle and Stanley, 1986). The identity of the Ter- millary masses in small cavities that are usually lined with quartz or lingua material with that from the Socrates mine was confirmed by chalcedony; and as hollow mammillary nodules as much as 3.4 mm comparison of its X-ray powder data with the unpublished X-ray in diameter with a wall thickness of 1.2 mrn (Fig. I). powder data previously submitted to the Commission on New Minerals The Terlingua specimen, which was purchased from Dr. F. Krantz, and Mineral Names, I.M.A. Subsequently, AJC wrote to the senior Bonn, Federal Republic of Germany, in 1906 by the British Museum author, and it was agreed that the chemical, optical and crystallographic (Natural History), consists of intergrown crystals of montroydite, data for the Terlingua material should be included in the present paper. terlinguaite, eglestonite and edgarbaileyite in cavities and fractures in Sufficient material was then available from both California and Texas a matrix of crystalline calcite, quartz and barite. Native mercury is for a comprehensive mineralogical study and full characterization; the also abundant within the cavities. For more information and references results are reported here. • on the Terlingua deposit, the reader is referred to Hill (1903), Yates We take great pleasure in naming this new mineral edgarbaileyite and Thompson (1959), Crook (1977), Roberts et al.