Hureaulite

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Hureaulite
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Hureaulite from the Cigana Claim, Conselheiro Pena, Minas Gerais, Brazil. Specimen size 2.8 cm.
General
Category Phosphate minerals
Formula
(repeating unit)		 Mn2+5(PO3OH)2(PO4)2·4H2O
Strunz classification 08.CB.10
7/C.04-10
Dana classification 39.2.1.1
Crystal symmetry Monoclinic 2/m
Unit cell a = 17.594(10) Å, b = 9.086(5) Å, c = 9.404(5) Å; α = 90°, β = 96.67(8)°, γ = 90°; Z = 4
Identification
Formula mass 728.65 g
Colour Orange, red, yellow, brown, grey or nearly colourless
Crystal habit Crystals are short prismatic parallel to (100) or equant, sometimes thick tabular, also massive or imperfectly fibrous[1]
Crystal system Monoclinic prismatic
Cleavage {100} good
Fracture Uneven
Tenacity Brittle
Mohs scale hardness 3.5
Luster Vitreous to greasy
Streak Nearly white
Diaphaneity Transparent to translucent
Specific gravity 3.18 - 3.2 (measured), 3.23 (calculated)
Optical properties Biaxial (-)
Refractive index nα = 1.640 – 1.654 nβ = 1.649 – 1.659 nγ = 1.655 – 1.662
Birefringence δ = 0.012
Pleochroism X colourless, Y yellow to pale rose, Z reddish yellow to reddish brown
2V angle greater than 60°
Dispersion r<v, very strong[2]
Solubility Easily soluble in acids.
References [2][3][4][5]

Hureaulite is a manganese phosphate with the formula Mn2+5(PO3OH)2(PO4)2·4H2O. It was discovered in 1825 and named in 1826 for the type locality, Les Hureaux, Saint-Sylvestre, Haute-Vienne, Limousin, France. It is sometimes written as huréaulite, but the IMA does not recommend this for English language text.[6]

A complete series exists from lithiophilite, LiMn2+PO4 to triphylite, LiFe2+PO4, including hureaulite, strengite, FePO4·2H2O, stewartite, Mn2+Fe3+2(OH,PO4)2·8H2O, and sicklerite, (LiMn2+,Fe3+)PO4.[7]

Environment

Hureaulite is a secondary mineral occurring in granite pegmatites.[5] At the type locality it occurs in a zone of altered triphylite, LiMn2+PO4, in pegmatite. Typically occurs very late in the sequence of formation of secondary phosphate minerals.[8] Associated at the type locality with vivianite, Fe2+3(PO4)2·8H2O; rockbridgeite, Fe2+Fe3+4(PO4)3(OH)5; heterosite, (Fe3+,Mn3+)PO4 and cacoxenite, Fe3+24AlO6(PO4)17(OH)12·17H2O. It can be synthesised;[9] most natural hureaulites are Mn-rich compounds but extensive (Mn,Fe) solution is known for synthetic material.[8]

Localities

The type locality is Les Hureaux, Saint-Sylvestre, Haute-Vienne, Limousin, France. Hureaulite is also found in a granite pegmatite known for its phosphates in the Aimorés pegmatite district, at the Cigana claim in Galiléia, Doce valley, Minas Gerais, Brazil, formerly known as the Jocão Mine.[3]

References

  1. ↑ Murdoch, Joseph (1942) Contributions to the Crystallography of Hureaulite. American Mineralogist 27: 228
  2. ↑ 2.0 2.1 Gaines et al (1997) Dana's New Mineralogy Eighth Edition
  3. ↑ 3.0 3.1 http://www.mindat.org/min-1952.html Mindat.org
  4. ↑ Shigley and Brown (1985) American Mineralogist 70:395
  5. ↑ 5.0 5.1 Roberts, Campbell and Rapp (1990) Encyclopedia of Minerals, 2nd edition
  6. ↑ Burke, E. A. J. (2008): Tidying up Mineral Names: An IMA scheme for Suffixes, Hyphens and Diacritical Marks. Mineralogical Record, 39, 134
  7. ↑ Murdoch, Joseph (1943) Crystallography of Hureaulite. American Mineralogist 28: 19-24
  8. ↑ 8.0 8.1 Moore, P B, and Araki, T (1973) Hureaulite: its atomic arrangement. American Mineralogist 58: 302-307.
  9. ↑ Gerault, Y, Riou, A, and Cudennec, Y (1987) Acta Crystallographica (C) 43:1829
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