Whiteite

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Whiteite is a rare hydrated phosphate mineral, with hydroxyl

Whiteite
Whiteite-Lazulite-48334.jpg
Whiteite with lazulite from Rapid Creek, Dawson Mining District, the Yukon, Canada
General
Category Phosphate Minerals
Formula
(repeating unit)

Whiteite-(CaFeMg):
CaFe2+Mg2Al2(PO4)4(OH)2·8H2O
Whiteite-(MnFeMg):
Mn2+Fe2+Mg2Al2(PO4)4(OH)2·8H2O
Whiteite-(CaMnMg):

CaMn2+Mg2Al2(PO4)4(OH)2·8H2O
Strunz classification

8.DH.15 (whole series) or
7/D.29-10 Whiteite-(CaFeMg)
7/D.29-30 Whiteite-(MnFeMg)

7/D.29-20 Whiteite-(CaMnMg)
Dana classification

42.11.3.1 Whiteite-(CaFeMg) 42.11.3.2 Whiteite-(MnFeMg)

42.11.3.3 Whiteite-(CaMnMg)
Identification
Formula mass

Whiteite-(CaFeMg):756.29g
Whiteite-(MnFeMg):767.44g

Whiteite-(CaMnMg):755.61g
Color

Whiteite-(CaFeMg): Brown, pink-brown or yellow
Whiteite-(MnFeMg): Brown

Whiteite-(CaMnMg): Yellow, light lavender or pink
Crystal habit Tabular crystals or aggregates thereof
Crystal system Monoclinic 2/m
Twinning Invariably twinned by reflection on {001} producing a pseudo-orthorhombic appearance
Cleavage On {001}. Poor for Whiteite-(CaMnMg), but good for the other members of the series (HOM)
Tenacity Whiteite-(CaMnMg) is brittle (HOM)
Mohs scale hardness 3 to 4
Luster Vitreous
Streak White to brownish white
Diaphaneity Translucent to transparent
Specific gravity

Whiteite-(CaFeMg) 2.58
Whiteite-(MnFeMg)2.67

Whiteite-(CaMnMg)2.63
Optical properties Biaxial (+)
Refractive index Nx = 1.580, Ny = 1.584 to 1.585, Nz = 1.590 to 1.591
Other characteristics Not radioactive
References

[1] [2] [3] [4] [5] [6] [7]

[8]

Whiteite subgroup[edit]

The name whiteite refers to three minerals in the jahnsite-whiteite group, whiteite subgroup. Subgroup members (formulae from IMA[8]):

  • Whiteite-(CaFeMg), IMA1975-001, CaFe2+Mg2Al2(PO4)4(OH)2·8H2O
  • Whiteite-(MnFeMg), IMA1978-A, Mn2+Fe2+Mg2Al2(PO4)4(OH)2·8H2O
  • Whiteite-(CaMnMg), IMA1986-012, CaMn2+Mg2Al2(PO4)4(OH)2·8H2O
  • Rittmannite, Mn2+Mn2+Fe2+2Al2(PO4)4(OH)2·8H2O

In the whiteite formulae, the symbols in brackets indicate the dominant atom in three distinct structural positions, designated X, M(1), and M(2), in that order; for instance, magnesium Mg is always the dominant atom in the M(2) position for all the whiteite minerals.[5] Whiteite was named after John Sampson White Jr (born 1933),[9] associate curator of minerals at the Smithsonian Institution, and founder, editor and publisher (1970-1982) of the Mineralogical Record.[10]

Unit cell[edit]

All members of the series belong to the monoclinic crystal system with point group 2/m. Most sources give the space group as P21/a for the Ca Fe rich member, which was the first of the series to be described,[6][2][5] but Dana gives it as P2/a.[1] The other members are variously described in different sources as having space groups P21/a, P2/a or Pa.

There are two formula units per unit cell (Z = 2). The cell parameters vary slightly between the group members, but to the nearest angstrom they all have a = 15 Å, b = 7 Å and c = 10 Å, with β 112.5 to 113.4. Individual values are:[1][2][3][4][5][6]

  • Whiteite-(CaFeMg) a = 14.90 Å, b = 6.98 Å, c = 10.13 Å, β = 113.12
  • Whiteite-(MnFeMg) a = 14.99 Å, b = 6.96 Å, c = 10.14 Å, β = 113.32
  • Whiteite-(CaMnMg) a = 14.842 Å, b = 6.976 Å, c = 10.109 Å, β = 112.59

Appearance[edit]

The whiteite minerals are generally brown, pink or yellow, and whiteite-(CaMnMg) may also be light lavender coloured.[5] They are transparent to translucent, with a vitreous luster and a white to brownish white streak. They occur as aggregates of tabular crystals, or thick tabular canoe-shaped crystals.[1] Whiteite from Rapid Creek in the Yukon, Canada, is often associated with deep blue lazulite crystals (33 out of 49 photos on Mindat).

Optical properties[edit]

The optical class is thought to be biaxial (+),[7][2][3][4] but whiteite-(CaFeMg) may be biaxial (-).[5][6] The refractive indices are Nx = 1.580, Ny = 1.584 to 1.585 and Nz = 1.590 to 1.591, similar to those for quartz.

Physical properties[edit]

Whiteite is invariably twinned, giving the crystals a pseudo-orthorhombic appearance,[1][5] and the cleavage is good to perfect.[5] Whiteite is quite soft, with hardness 3 to 4, between calcite and fluorite. Its specific gravity is 2.58, similar to that of quartz.[1][2] [3][4][5][6] Whiteite is not radioactive.[2][3] [4]

Occurrence[edit]

The type locality for whiteite-(CaFeMg)and whiteite-(MnFeMg) is the Ilha claim, Taquaral, Itinga, Jequitinhonha valley, Minas Gerais, Brazil, and for whiteite-(CaMnMg) it is the Tip Top Mine (Tip Top pegmatite), Fourmile, Custer District, Custer County, South Dakota, USA.[7] The type material is conserved at the National School of Mines, Paris, France, and at the National Museum of Natural History, Washington DC, USA, reference 123013.[5]
At the Lavra da Ilha pegmatite, Taquaral, Brazil, whiteite is found in a complex zoned granite pegmatite associated with eosphorite, zanazziite, wardite, albite and quartz.[5] At Blow River, the Yukon, Canada, it is found in iron-rich sedimentary rocks with siderite, lazulite, arrojadite and quartz.[5] At Ilha de Taquaral, Minas Gerais, Brazil, it occurs along joints and fractures in quartz and albite associated with other phosphates.[6]

References[edit]

  1. ^ a b c d e f Gaines et al (1997) Dana’s New Mineralogy Eighth Edition. Wiley
  2. ^ a b c d e f "Whiteite-(CaFeMg) Mineral Data". Webmineral.com. Retrieved 2012-03-15. 
  3. ^ a b c d e "Whiteite-(MnFeMg) Mineral Data". Webmineral.com. Retrieved 2012-03-15. 
  4. ^ a b c d e "Whiteite-(CaMnMg) Mineral Data". Webmineral.com. Retrieved 2012-03-15. 
  5. ^ a b c d e f g h i j k l "Handbook of Mineralogy". Handbook of Mineralogy. Retrieved 2012-03-15. 
  6. ^ a b c d e f Fleischer, Chao and Pabst (1979) American Mineralogist 64:465, summarising Moore and Ito (1978) Mineralogical Magazine 42:309 [Whiteite-(CaMnMg) - AM75: Jambor and Grew (1990) American Mineralogist 75:933, summarising Grice, Dunn and Ramik (1989) The Canadian Mineralogist 27:699]
  7. ^ a b c "Whiteite-(CaFeMg): Whiteite-(CaFeMg) mineral information and data". Mindat.org. 2012-01-30. Retrieved 2012-03-15. 
  8. ^ a b "IMA Mineral List with Database of Mineral Properties". Rruff.info. Retrieved 2012-03-15. 
  9. ^ "Label Archive". The Mineralogical Record. 1933-09-30. Retrieved 2012-03-15. 
  10. ^ "The Mineralogical Record". The Mineralogical Record. Retrieved 2012-03-15.