Eosphorite

Eosphorite is a brown (occasionally pink) manganese hydrous phosphate mineral with chemical formula: MnAl(PO4)(OH)2·H2O.[4] It is used as a gemstone.[5]

Eosphorite
General
CategoryPhosphate mineral
Formula
(repeating unit)
MnAl(PO4)(OH)2·H2O
Strunz classification8.DD.20
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupCmca
Unit cella = 10.455(1), b = 13.501(2)
c = 6.928(1) [Å]; β = 90°; Z = 8
Identification
Colorusually pale brown, golden brown, also medium brown to dark brown; occasionally pink, rose red
Crystal habitPrismatic in radiating sprays or spheres, massive; twinned pseudo-orthorhombic
TwinningMay be observed on {100} and {001}
CleavagePoor on {100}
FractureSubconchoidal to uneven
Mohs scale hardness5
LusterVitreous, resinous
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity3.06 – 3.08
Optical propertiesBiaxial (-)
Refractive indexnα = 1.628 - 1.639 nβ = 1.648 - 1.664 nγ = 1.657 - 1.671
Birefringenceδ = 0.029 - 0.032
PleochroismVisible: X = yellow; Y = pink; Z = pale pink to colorless
2V angleMeasured: 50°
Alters toOxidizes to brown or black
References[1][2][3]

Eosphorite crystallizes in the monoclinic crystal system. It forms slender prismatic crystals which often form radiating or spherical clusters. The crystals often show pseudo–orthorhombic forms due to twinning.[3]

Eosphorite forms a series with childrenite, the iron rich member, with divalent iron replacing most of the manganese in the crystal lattice. The two endmembers are isostructural but differ in their properties, such as crystal habit, coloration, and optical properties.

It was first described in 1878 for an occurrence in the Branchville Mica Mine in Branchville, Fairfield County, Connecticut, US. Its name is derived from the Greek έωσφορος for "dawn-bearing," because of its pink color.[2] It occurs worldwide typically as a secondary mineral in phosphate rich granitic pegmatites in association with rhodochrosite, lithiophilite, triphylite, triploidite, dickinsonite, albite, cookeite, apatite, beryllonite, hydroxyl-herderite, and tourmaline.[3] An attractive combination of eosphorite and rose quartz occurs at Taquaral, Minas Gerais, Brazil.[6]

References

  1. Eosphorite, WebMineral.com, retrieved 2011-01-30
  2. Eosphorite, MinDat.org, retrieved 2011-01-30
  3. Handbook of Mineralogy
  4. Fleischer, Michael & Mandarino, Joseph, "Glossary of Mineral Species", The Mineralogical Record, 1991
  5. Gemstones By Michael O'Donoghue p.192
  6. http://www.galleries.com/Eosphorite
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