Metazeunerite

Metazeunerite is an arsenate mineral with a chemical formula of Cu(UO2)2(AsO4)2·8H2O. The origin of this mineral is almost always from the natural dehydration process of zeunerite. [4]

Metazeunerite
Metazeunerite crystals to 7 mm on smoky quartz, Erongo Region, Namibia
General
CategoryPhosphate minerals
Formula
(repeating unit)		Cu(UO2)2(AsO4)2·8H2O
Strunz classification8.EB.10
Crystal systemTetragonal
Crystal classDipyramidal (4/m)
(same H-M symbol)
Space groupP4/n
Unit cella = 7.1094 Å, c = 17.416 Å;
Z = 2
Identification
ColorVaries from pale to green
Crystal habitTabular rectangular crystals with two pinacoid faces; foliated or micaceous aggregates
TwinningMerohedrally twinned
CleavagePerfect on {001}; distinct on {010}
FractureUneven
TenacityBrittle
Mohs scale hardness2-2.5
LusterVitreous to dull
StreakPale green
DiaphaneityTransparent to translucent
Specific gravity3.87
Optical propertiesUniaxial(-)
Refractive indexnw=1.643-1.651 nε=1.623-1.635
Birefringence.020
PleochroismWeak
SolubilitySoluble in acids
Other characteristics Radioactive,
Relief: moderate
References[1][2][3]

Named for civil engineer Gustav A. Zeuner who worked at the School of Mines in Freiberg and its lowered hydration state.[3]

Properties

Its crystal system is tetragonal and its crystal class is 4/m, which is also called the tetragonal-dipyramidal class because it only has a vertical four-fold rotation axis that is perpendicular to the symmetry plane.[5][6] When looking at a thin section, metzeunerite is anisotropic, meaning that it has pleochroism. When a mineral is anisotropic, one can see whether it is uniaxial or biaxial, depending on how fast the rays of light are moving through the mineral. This mineral is uniaxial negative due to the ordinary ray being slower than the extraordinary ray.[7]

Occurrence

Metazeunerite is an uncommon radioactive secondary mineral found in "arsenic bearing hydrothermal uranium deposits" across the world.[8] This widespread mineral occurs specifically in Europe, western North America, Australia, Brazil and Chile, Namibia, and Kazakhstan.[3] It is currently studied through thermal decomposition by calculating the different levels of dehydration, as zeunerite is transformed into metazeunerite.[9] Metazeunerite was shown to be an important solubility limiting phase controlling uranium migration in the soils of the UK's only, and now abandoned, uranium mine, South Terras, located near St Stephen-in-Brannel.[10]

References
  1. Mineralienatlas
  2. Metazeunerite Mineral Data Webmineral
  3. Metazeunerite on Mindat
  4. Amethyst Galleries
  5. Roberts, W., Campbell, T., and Rapp, G. (1990) Encyclopedia of Minerals (Second Edition), 558 p. Van Nordstrand Reinhold, New York.
  6. Klein, C., and Dutrow, B. (2007) The 23rd Edition of the Manual of Mineral Science (23rd edition), 194 p. John Wiley & Sons, Inc.
  7. "Optical Properties of Minerals." University of North Dakota
  8. "Metazeunerite." Mineral Data Publishing, 2005
  9. Frost, Ray L; Weier, Matt L; Adebajo, Moses O (2004), "Thermal Decomposition of Metazeunerite—a High-resolution Thermogravimetric and Hot-stage Raman Spectroscopic Study" (PDF), Thermochimica Acta, 419 (1–2): 119–129, doi:10.1016/j.tca.2004.02.006
  10. Corkhill, Claire L.; Crean, Daniel E.; Bailey, Daniel J.; Makepeace, Carmen; Stennett, Martin C.; Tappero, Ryan; Grolimund, Daniel; Hyatt, Neil C. (2017-12-14). "Multi-scale investigation of uranium attenuation by arsenic at an abandoned uranium mine, South Terras". NPJ Materials Degradation. 1 (1). doi:10.1038/s41529-017-0019-9. ISSN 2397-2106.

Bibliography
  • Palache, P.; Berman H.; Frondel, C. (1960). "Dana's System of Mineralogy, Volume II: Halides, Nitrates, Borates, Carbonates, Sulfates, Phosphates, Arsenates, Tungstates, Molybdates, Etc. (Seventh Edition)" John Wiley and Sons, Inc., New York, pp. 993-994.
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