Magnesiopascoite

Magnesiopascoite
General
Category Vanadate minerals
Formula
(repeating unit)		 Ca2Mg(V10O28)·16H2O
Strunz classification 4.HC.05[1]
Dana classification 47.3.6.3[1]
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group C2/m
Unit cell a = 19.8442 Å,
b = 9.9353 Å,
c = 10.7149 Å
β = 120.305°; Z = 2
Identification
Color Bright orange
Twinning None observed[1]
Cleavage Perfect on {001}
Fracture Conchoidal, curved
Tenacity Brittle
Mohs scale hardness 2.5
Luster Adamantine
Streak Yellow
Diaphaneity Transparent
Optical properties Biaxial (-)
Refractive index nα = 1.769(3)
nβ = 1.802(3)
nγ = 1.807(3)[1]
Birefringence δ = 0.038[1]
2V angle 45° (measured)
Dispersion r < v, crossed[1]
Solubility Slowly in water
Quickly in cold, dilute HCl[2]
References [3][4]

Magnesiopascoite is a bright orange mineral with formula Ca2Mg(V10O28)·16H2O. It was discovered in the U.S. state of Utah and formally described in 2008. The mineral's name dervies from its status as the magnesium analogue of pascoite.

Description

Magnesiopascoite is a member of the pascoite group and is the magnesium analogue of pascoite.[2] It is transparent and bright orange in color,[4] occurring as intergrown, parallel stackings of crystals up to several millimeters in the largest dimension.[2][4] The crystals vary from tabular to equant to prismatic.[2][4] The mineral dissolves slowly in water and quickly in cold, dilute hydrochloric acid. It decomposes rapidly when mildly heated, likely as a result of dehydration.[2]

Structure and composition

The crystal structure of magnesiopascoite consists of the decavanadate anion (V10O28)6− and interstitial {Ca2Mg(H2O)16}6+ consisting of Mg(H2O)6 octahedra and seven-fold coordinated CaO2(H2O)5.[5] The structure differs from that of pascoite primarily in cation coordination in the interstitial complex.[6] In addition to calcium and magnesium, magnesiopascoite contains minute quantities of zinc and cobalt.[7]

History

Joe Marty discovered specimens of magnesiopascoite in San Juan County, Utah, in the Blue Cap mine and the nearby Vanadium Queen mine.[2] The mineral was named "magnesiopascoite" because it is the magnesium analogue of pascoite.[4] The mineral and name were approved by the IMA Commission on New Minerals, Nomenclature and Classification (IMA 2007-025).[2] Magnesiopascoite was described in 2008 in the journal Canadian Mineralogist.[8] The two cotype specimens are held at the Natural History Museum of Los Angeles County in the US State of California.[2]

Occurrence

In the area of the type locality, the reducing environment caused by carbonaceous material in the Salt Wash and Brushy Basin members of the Morrison Formation precipitated uranium and vanadium minerals from solution. After mining, subsequent leaching and oxidation by groundwater created magnesiopascoite.[2] The mineral has been found in association with gypsum, martyite, montroseite, pyrite and rossite.[4]

References

  1. 1 2 3 4 5 6 "Magnesiopascoite". Mindat.org. Retrieved July 21, 2012.
  2. 1 2 3 4 5 6 7 8 9 Kampf & Steele 2008, p. 680.
  3. ↑ Mineralienatlas
  4. 1 2 3 4 5 6 "Magnesiopascoite" (PDF). Handbook of Mineralogy. Mineralogical Society of America. Retrieved July 21, 2012.
  5. ↑ Kampf & Steele 2008, pp. 682–683.
  6. ↑ Kampf & Steele 2008, p. 683.
  7. ↑ Kampf & Steele 2008, p. 681.
  8. ↑ Kampf & Steele 2008, p. 679.

Bibliography

  • Kampf, Anthony R.; Steele, Ian M. (June 2008). "Magnesiopascoite, a new member of the pascoite group: description and crystal structure". Canadian Mineralogist. 46 (3): 679–686. doi:10.3749/canmin.46.3.679. (subscription required)
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