Chemistry:Mansfieldite

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Mansfieldite
Mansfieldite.jpg
General
CategoryMineral
Formula
(repeating unit)
AlAsO4·2H2O
Strunz classification08.CD.10
Dana classification40.04.01.04
Crystal systemOrthorhombic
Crystal classOrthorhombic-Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupPbca
Unit cell876.8 ų
Identification
Formula mass201.93 gm
ColorWhite, light gray
Crystal habitSpherical, encrustations
CleavageIndistinct on {201} and on {001} and {100} in traces
FractureSub-conchoidal
Mohs scale hardness3.5–4
|re|er}}Vitreous
StreakWhite
DiaphaneityTransparent, transculent
Specific gravity3.03
Density3.03
Optical propertiesBiaxial (+)
Refractive indexnα = 1.622 – 1.631 nβ = 1.624 – 1.649 nγ = 1.642 – 1.663
Birefringence0.020 – 0.032
2V angleMeasured 30°–68°, calculated 38°–82°
DispersionNone
Common impuritiesCobalt

Mansfieldite is an uncommon mineral that was named after an American geologist, George Rogers Mansfield. It has been considered a valid specie since 1948. It is a member of the variscite group. Mansfieldite creates a series with scorodite, and it is the aluminium analogue of said gem. Mansfieldite is colorless in transmitted light.[2] It is mostly made out of oxygen (47.54%). Other components include arsenic (37.1%), aluminium (13.36%) and hydrogen (2%).[3] Mansfieldite crystals form due to hydrothermal origin in altered and mineralized andesitic pyroclastic rocks. Due to its size, mansfieldite is hard to see even under a microscope. The pink variation of the mineral is due to cobalt impurities, otherwise it is white to light gray. It can be found in the US, Mexico, France, Algeria, England, Australia, Germany, Algeria and Kazakhstan.[4]

References