Chemistry:Hureaulite

Hureaulite
Hureaulite from the Cigana Claim, Conselheiro Pena, Minas Gerais, Brazil. Specimen size 2.8 cm.
General
Category	Phosphate minerals
Formula (repeating unit)	Mn2+ 5(PO 3OH) 2(PO 4) 2 · 4H2O
Strunz classification	8.CB.10 (10 ed) 7/C.04-10 (8 ed)
Dana classification	39.2.1.1
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/c
Unit cell	a = 17.594(10) Å b = 9.086(5) Å c = 9.404(5) Å β = 96.67(8)°; Z = 4
Identification
Formula mass	728.65 g/mol
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
Cleavage	{100} good
Fracture	Uneven
Tenacity	Brittle
Mohs scale hardness	3.5
Vitreous to greasy|re|er}}	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
Solubility	Easily soluble in acids.
References

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.

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.

Environment

Hureaulite is a secondary mineral occurring in granite pegmatites. 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. 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; most natural hureaulites are Mn-rich compounds but extensive (Mn,Fe) solution is known for synthetic material.

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.