Home The first occurrence of the carbide anion, C4–, in an oxide mineral: Mikecoxite, ideally (CHg4)OCl2, from the McDermitt open-pit mine, Humboldt County, Nevada, U.S.A
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The first occurrence of the carbide anion, C4–, in an oxide mineral: Mikecoxite, ideally (CHg4)OCl2, from the McDermitt open-pit mine, Humboldt County, Nevada, U.S.A

  • Mark A. Cooper , Gail Dunning , Frank C. Hawthorne , Chi Ma ORCID logo , Anthony R. Kampf ORCID logo , John Spratt , Christopher J. Stanley and Andrew G. Christy
Published/Copyright: March 2, 2023
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American Mineralogist
From the journal American Mineralogist Volume 108 Issue 3

Abstract

Mikecoxite, ideally (CHg4)OCl2, is the first mercury-oxide-chloride-carbide containing a C4– anion coordinated by four Hg atoms (a permercurated methane derivative) to be described as a mineral species. It was found at the McDermitt open-pit mine on the eastern margin of the McDermitt Caldera, Humboldt County, Nevada, U.S.A. It is monoclinic, space group P21/n, Z = 4; a = 10.164(5), b = 10.490(4), c = 6.547(3) Å, V 698.0(5) Å3. Chemical analysis by electron microprobe gave Hg 86.38, Cl 11.58, Br 0.46, C 1.81, sum = 100.23 wt%, and O was detected but the signal was too weak for quantitative chemical analysis. The empirical formula, calculated on the basis of Hg + Cl + Br = 6 apfu, is (C1.19Hg3.39)(Cl2.57Br0.05)Σ2.62, and the ideal formula based on the chemical analysis and the crystal structure is (CHg4)OCl2. The seven strongest lines in the X-ray powder diffraction pattern are [d (Å), I, (hkl)]: 2.884, 100, (230); 2.989, 81, (301, 301, 112, 112, 131, 131); 2.673, 79, (122, 122, 212, 212); 1.7443, 40, (060, 432, 432); 5.49, 34, (101, 101); 4.65, 32, (120); 2.300, 30, (312, 312). The Raman spectrum shows three bands at 638, 675, and 704 cm–1, well above the range characteristic of NHg4 stretching vibrations between 540 and 580 cm–1, that are assigned to CHg4 stretching vibrations. Mikecoxite forms intergrowths of bladed crystals up to 100 μm long that occur on granular quartz or in vugs associated with kleinite. It is black with a submetallic to metallic luster and strong specular reflections and does not fluoresce under short- or long-wave ultraviolet light. Neither cleavage nor parting were observed, and the calculated density is 8.58 g/cm3. In the crystal structure of mikecoxite, ( C 4 − H g 4 2 + ) groups link through O2– ions to form three-membered rings that polymerize into corrugated [CHg4OCl]+ layers with near-linear C4––Hg2+–O and C4––Hg2+–Cl linkages. The layers link in the third direction directly via weak Hg2+–O2– and Hg2+–Cl– bonds to adjacent layers and also indirectly via interlayer Cl–. A bond-valence parameter has been derived for (Hg2+–C4–) bonds: Ro = 2.073 Å, b = 0.37, which gives bond-valence sums at the C4– ions in accord with the valence-sum rule. The source of carbon for mikecoxite in the volcanic high-desert environment of the type locality seems to be methane, with the reaction catalyzed by microbiota through full mercuration of carbon atoms, beyond the first stage that produces the volatile and highly mobile methylmercury, [CH3Hg]+, a potent neurotoxin that accumulates in marine food chains. Both the mineral and the mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2021-060). The mineral is named after Michael F. Cox (b. 1958), a founding member of the New Almaden Quicksilver County Park Association (NAQCPA) who was responsible for characterizing and remediating environmental mercury on-site and who recovered the rock containing the new mineral.

Keywords: Mikecoxite; new mineral; mercury-oxide-chloride-carbide; crystal-structure refinement; Raman spectrum; electron-microprobe analysis; McDermitt open-pit mine; Humboldt County; Nevada; U.S.A.

§ Deceased.

Acknowledgments and Funding

We thank the reviewers for their comments. Financial support for this work came from the Natural Sciences and Engineering Research Council of Canada in the form of a Canada Research Chair in Crystallography and Mineralogy, and a Discovery grant to F.C.H., and by Canada Foundation for Innovation grants to F.C.H.

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Received: 2021-12-07
Accepted: 2022-04-01
Published Online: 2023-03-02
Published in Print: 2023-03-28

© 2023 by Mineralogical Society of America

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https://doi.org/10.2138/am-2022-8408
Keywords for this article
Mikecoxite; new mineral; mercury-oxide-chloride-carbide; crystal-structure refinement; Raman spectrum; electron-microprobe analysis; McDermitt open-pit mine; Humboldt County; Nevada; U.S.A.

Articles in the same Issue

  1. Mineralogy and bulk geochemistry of a fumarole at Hverir, Iceland: Analog for acid-sulfate leaching on Mars
  2. The crystal structure and chemistry of natural giniite and implications for Mars
  3. Solid solution of CaSiO3 and MgSiO3 perovskites in the lower mantle: The role of ferrous iron
  4. Secondary ion mass spectrometer analyses for trace elements in glass standards using variably charged silicon ions for normalization
  5. Raman shifts of c-BN as an ideal P-T sensor for studying water-rock interactions in a diamond-anvil cell
  6. Resetting of the U-Pb and Th-Pb systems in altered bastnäsite: Insight from the behavior of Pb at nanoscale
  7. X-ray diffraction reveals two structural transitions in szomolnokite
  8. Contamination of heterogeneous lower crust in Hannuoba tholeiite: Evidence from in situ trace elements and strontium isotopes of plagioclase
  9. Oxygen fugacity buffering in high-pressure solid media assemblies from IW-6.5 to IW+4.5 and application to the V K-edge oxybarometer
  10. Trace element partitioning between anhydrite, sulfate melt, and silicate melt
  11. Chemical reaction between ferropericlase (Mg,Fe)O and water under high pressure-temperature conditions of the deep lower mantle
  12. Composition-dependent thermal equation of state of B2 Fe-Si alloys at high pressure
  13. Effects of thermal annealing on water content and δ18O in zircon
  14. Tourmaline and zircon trace the nature and timing of magmatic-hydrothermal episodes in granite-related Sn mineralization: Insights from the Libata Sn ore field
  15. Cation ordering, twinning, and pseudo-symmetry in silicate garnet: The study of a birefringent garnet with orthorhombic structure
  16. The occurrence of monoclinic jarosite in natural environments
  17. Niobium speciation in minerals revealed by L2,3-edges XANES spectroscopy
  18. The first occurrence of the carbide anion, C4–, in an oxide mineral: Mikecoxite, ideally (CHg4)OCl2, from the McDermitt open-pit mine, Humboldt County, Nevada, U.S.A
  19. Hydrothermal alteration of Ni-rich sulfides in peridotites of Abu Dahr, Eastern Desert, Egypt: Relationships among minerals in the Fe-Ni-Co-O-S system, fO2 and fS2
  20. New Mineral Names: Arsenic and Lead
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