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Formula: CaMn2+5 (V2O7)3.12H2O
Hydrated divanadate,
manganese-bearing mineral
Crystal System: Monoclinic
Specific gravity: 2.74 measured, 2.744 calculated for the empirical formula and 2.695 calculated for the ideal formula
Hardness: 2
Streak: Light pinkish orange
Colour: Orangish red
Luminescence: No fluorescence under UV
Environments
Sedimentary environments
Hydrothermal environments
Localities
At the type Locality, the Packrat Mine, Beaver Mesa, Gateway Mining District, Mesa County, Colorado, USA,
mesaite was found in the main tunnel level of the mine on asphaltum (bitumen) blocks associated with
montroseite- and corvusite-
bearing sandstone. Other
secondary minerals found in close association with
mesaite are ansermetite,
kegginite, martyite,
morrisonite,
rossite/metarossite and
sherwoodite.
Other secondary minerals found in the mine include
andersonite, calcite,
dickthomssenite,
gatewayite, gypsum,
hewettite, hummerite,
lasalite, magnesiopascoite,
martyite, munirite,
navajoite, packratite,
pascoite, pharmacolite,
picropharmacolite, postite,
selenium, uranopilite and
vanarsite.
Mesaite forms from the oxidation of
montroseite-corvusite
assemblages in a moist environment. Mining operations have exposed both unoxidised and oxidised phases. Under ambient
temperatures and generally oxidising near-surface conditions, water reacts with
pyrite and an unknown arsenic-bearing
phase (perhaps arsenopyrite) to form aqueous solutions with relatively
low pH (acid). The various secondary
vanadate phases that form depend upon prevailing conditions and the presence
of other cations such as Na+, Ca2+ and Mn2+.
Mesaite crystals occur as blades up to 0.1 mm long and ∼10 μm thick indivergent sprays. The crystals are
orangish red and brownish orange and transparent in transmitted light. The streak is light pinkish orange and the
lustre is vitreous
(MM 81>2.319-327).
Mesaite from the Packrat Mine - Image
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