Eosphorite

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Eosphorite
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General
Category Phosphate mineral
Formula
(repeating unit)
MnAl(PO4)(OH)2·H2O
Strunz classification 8.DD.20
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Cmca
Unit cell a = 10.455(1), b = 13.501(2)
c = 6.928(1) [Å]; β = 90°; Z = 8
Identification
Color usually pale brown, golden brown, also medium brown to dark brown; occasionally pink, rose red
Crystal habit Prismatic in radiating sprays or spheres, massive; twinned pseudo-orthorhombic
Twinning May be observed on {100} and {001}
Cleavage Poor on {100}
Fracture Subconchoidal to uneven
Mohs scale hardness 5
Luster Vitreous, resinous
Streak White
Diaphaneity Transparent to translucent
Specific gravity 3.06 – 3.08
Optical properties Biaxial (-)
Refractive index nα = 1.628 - 1.639 nβ = 1.648 - 1.664 nγ = 1.657 - 1.671
Birefringence δ = 0.029 - 0.032
Pleochroism Visible: X = yellow; Y = pink; Z = pale pink to colorless
2V angle Measured: 50°
Alters to Oxidizes to brown or black
References [1][2][3]

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 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[edit]

  1. ^ Eosphorite, WebMineral.com, retrieved 2011-01-30 
  2. ^ a b Eosphorite, MinDat.org, retrieved 2011-01-30 
  3. ^ a b c 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