Hureaulite

Hureaulite is a manganese phosphate with the formula Mn2+
5(PO
3OH)
2(PO
4)
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]

Hureaulite
Hureaulite from the Cigana Claim, Conselheiro Pena, Minas Gerais, Brazil. Specimen size 2.8 cm.
General
CategoryPhosphate minerals
Formula
(repeating unit)		Mn2+
5(PO
3OH)
2(PO
4)
2·4H2O
Strunz classification8.CB.10 (10 ed)
7/C.04-10 (8 ed)
Dana classification39.2.1.1
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupC2/c
Unit cella = 17.594(10) Å
b = 9.086(5) Å
c = 9.404(5) Å
β = 96.67(8)°; Z = 4
Identification
Formula mass728.65 g/mol
ColourOrange, red, yellow, brown, grey or nearly colourless
Crystal habitCrystals are short prismatic parallel to (100) or equant, sometimes thick tabular, also massive or imperfectly fibrous[1]
Cleavage{100} good
FractureUneven
TenacityBrittle
Mohs scale hardness3.5
LustreVitreous to greasy
StreakNearly white
DiaphaneityTransparent to translucent
Specific gravity3.18 - 3.2 (measured), 3.23 (calculated)
Optical propertiesBiaxial (-)
Refractive indexnα = 1.640 – 1.654 nβ = 1.649 – 1.659 nγ = 1.655 – 1.662
Birefringenceδ = 0.012
PleochroismX colourless, Y yellow to pale rose, Z reddish yellow to reddish brown
2V anglegreater than 60°
Dispersionr<v, very strong[2]
SolubilityEasily soluble in acids.
References[2][3][4][5]

A complete series exists from lithiophilite, LiMn2+PO
4 to triphylite, LiFe2+PO
4, including hureaulite, strengite, FePO
4·2H2O, stewartite, Mn2+Fe3+
2(OH,PO
4)
2·8H2O, and sicklerite, (LiMn2+,Fe3+)PO
4.[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+PO
4, 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(PO
4)
2·8H2O; rockbridgeite, Fe2+Fe3+
4(PO
4)
3(OH)
5; heterosite, (Fe3+,Mn3+)PO
4 and cacoxenite, Fe3+
24AlO
6(PO
4)
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. Gaines et al (1997) Dana's New Mineralogy Eighth Edition
  3. http://www.mindat.org/min-1952.html Mindat.org
  4. Shigley and Brown (1985) American Mineralogist 70:395
  5. 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. 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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