Ophirite
Ophirite | ||
---|---|---|
General | ||
Category | Specific gravity 4.060 g/cm3 | |
Optical properties | Biaxial positive | |
Refractive index | nα= 1.730(3) nβ= 1.735(3) nγ= 1.770(3) | |
Birefringence | δ = 0.040 | |
Pleochroism | Visible | |
Dispersion | r > v, strong | |
Ultraviolet fluorescence | None | |
References | [2][3] |
Ophirite is a
Occurrence
Ophirite is found in association with scheelite and pyrite. The production of the mineral is thought to be from oxidative alteration of sulfides: a reaction between dolomite and scheelite with oxidizing and late acidic hydrothermal solutions that are in the presence of calcium-rich and pyrite hornfels. It occurs in one veinlet, which is surrounded by sphalerite, galena, bournonite, unidentified sulfide minerals, foci of apatite, and sericite-containing pyrite, and is typically interface between scheelite and dolomite. Also present in the vein are crystals of sulfur and fluorite.[2]
Physical properties
Ophirite is an orange-brown, transparent mineral with a vitreous luster. It exhibits a hardness of 2 on the
Optical properties
Ophirirte is biaxial positive, which means it will refract light along two axes. The mineral is optically biaxial positive, 2Vmeas. 43(2)°. The refractive indices are: α ~ 1.730(3), β ~ 1.735(3), and γ ~ 1.770(3)°. Dispersion is strong, r > v. Its pleochroism is light orange brown for X and Y, and orange brown for Z, where X<Y<<Z. Observations indicate that chemical species are in their fully oxidized states.[2]
Chemical properties
Ophirite is a tungstate, and is the first mineral discovered containing [4]Fe3+[6]W6+9O34, a group in the structural unit of the ophirite polyanion. Tri-lacunary Keggin anions are well known in synthetic compounds, but ophirite is the first known example of a mineral with a tri-lacunary Keggin polyanion.The empirical chemical formula for ophirite calculated on the basis of 30 cations, is Ca1.73Mg3.99[Zn2.02Mn3+1.82(H2O)2(Fe3+2.34W17.99O68)2] · 45.95•H2O. The ideal formula for ophirite is Ca2Mg4[Zn2Mn3+2(H2O)2(Fe3+W9O34)2] · 46•H2O.[2]
Chemical composition
Constituent | wt% | ideal wt% |
---|---|---|
CaO | 1.68 | 1.94 |
MgO | 2.79 | 2.78 |
ZnO | 2.86 | 2.81 |
Mn2O3 | 2.50 | 2.73 |
Fe2O3 | 3.25 | 2.76 |
Sb2O3 | 0.61 | - |
WO3 | 71.94 | 72.06 |
H2O | 15.24 | 14.92 |
Total | 100.87 | 100.00 |
X-ray crystallography
A Rigaku R-Axis Rapid II curved imaging plate microdiffractometer using monochromatized MoKα radiation was used to collect X-ray diffraction data for ophirite.
See also
References
- S2CID 235729616.
- ^ a b c d e f g Anthony R. Kampf, John M. Hughes, Barbara P. Nash, Stephen E. Wright, George R. Rossman, Joe Marty; Ophirite, Ca2Mg4[Zn2Mn23+(H2O)2(Fe3+W9O34)2]·46H2O, a new mineral with a heteropolytungstate tri-lacunary Keggin anion. American Mineralogist 2014;; 99 (5-6): 1045–1051. doi: https://doi.org/10.2138/am.2014.4699.
- ^ a b c Hudson Institute of Mineralogy, 2014, Ophirite: https://www.mindat.org/min-43845.html (accessed November 2023)