Mosesite

Mosesite is a very rare mineral found in few locations. It is a mercury mineral found as an accessory in deposits of mercury, often in conjunction with limestone. It is known to be found in the U.S. states of Texas and Nevada, and the Mexican states of Guerrero and Querétaro. It was named after Professor Alfred J. Moses for his contributions to the field of mineralogy in discovering several minerals found alongside mosesite. The mineral itself is various shades of yellow and a high occurrence of spinel twinning. It becomes isotropic when heated to 186 °C (367 °F).

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Composition

Mosesite contains 16 Hg, 3 Cl, 1½ SO₄, ½ CO₃ , ½ MoO₄, 16 H, and 8 N with a volume of 8.4777x10⁻¹ nm³ and calculated density of 7.53 g/cm³. The accepted formula for mosesite is Hg₂N(Cl,SO₄,MoO₄,CO₃)•H₂0.

Geologic occurrence

Discovered in a mercury mine in Terlingua, Texas, mosesite has also been seen in Nevada and Mexico. Mosesite is a secondary mineral formed at low temperature in hydrothermal mercury deposits. The mercury ore at the mine in Huahuaxtla is aligned with ribs of brecciated limestone that formed along shallow angle fault plane. In the Huahuaxtla mine, this is due to the evidence of oxidized minerals. The portion of the mine in which the mosesite was found is thought to be a solution cavity in a zone of fractured limestone. Mosesite is never found in abundance in any of the known locations of its origin.

Structure

Spinel twinning is a common occurrence in mosesite. Mosesite was found to have a unit cell with diamond type space lattice and the measured unit cube of Mosesite was approximately 9.44 nmx10⁻¹ with additional forms {001}, {011}, {116}, {114}, and {112}. In Mexico, the mosesite was most usually found as octahedral crystals which were usually intergrown. Single crystals are rare. Mosesite has a similar structure to Millon’s base (Hg₂NOH•nH₂0). Mosesite consists of a three-dimensional framework of Hg₃N⁺ groups. The mercury atoms form linear sp bonds, while the nitrogen forms tetrahedral sp3 bonds, in a face-centered cubic lattice. The space group of mosesite is F*43m.

Physical properties

Mosesite is a minute yellow crystal with imperfect cleavage along {111} and uneven fracture. It is brittle with a hardness of 3.5. Long exposure, a month or more, to light will change Mosesite to a light olive green. The powdered form retains its color streaking a light yellow. The mineral exhibits no pleochroism and displays uneven birefringence in polarized light. Heat has a notable effect on Mosesite for when heated above 186 °C (367 °F) the mineral becomes isotropic. This corresponds optically with the observed crystal form only at this higher temperature. It is considered weakly anisotropic. The index of refraction is n = 2.065±0.01. It has an adamantine luster officially ranges in color from lemon yellow to canary yellow. Mosesite reacts chemically with HCl leaving a residue of HgCl.

References

• Bird, 1932 Paul H. Bird, A New Occurrence and X-ray Study of Mosesite, American Mineralogist 17 (12) (1932), pp. 541-550.
• Canfield et al. 1910 F.A. Canfield, W.F. Hillebrand, W.T. Schaller, Mosesite, a New Mercury Mineral from Terlingua, Texas, American Journal of Science 30 (1910), pp. 202-208.
• Luquer, 1920 Lea McI. Luquer, Alfred J. Moses, American Mineralogist 5 (6) (1920), pp. 109-112.
• Switzer et al., 1953 George S. Switzer, W.F. Foshag, K.J. Murata, J.J. Fahey, Re-Examination of Mosesite, American Mineralogist 38 (11-12), pp. 1225-1234.