| Hureaulite | |
|---|---|
Hureaulite from the Cigana Claim, Conselheiro Pena, Minas Gerais, Brazil. Specimen size 2.8 cm. |
|
| General | |
| Category | Phosphate minerals |
| Chemical formula | Mn2+5(PO3OH)2(PO4)2·4H2O |
| Strunz classification | 7/C.04-10 or 8.CB.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 | |
| Molar mass | 728.65 g |
| Color | 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]
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]
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]