Whiteite
| Whiteite | |
|---|---|
 | |
| General | |
| Category | Phosphate minerals |
| Formula (repeating unit) | Whiteite-(CaFeMg): CaFe2+Mg2Al2(PO4)4(OH)2·8H2O |
| Strunz classification | 8.DH.15 (10 ed, whole series) 7/D.29 (8 ed) |
| Dana classification | 42.11.3.1 Whiteite-(CaFeMg)
42.11.3.2 Whiteite-(MnFeMg) 42.11.3.3 Whiteite-(CaMnMg) |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | P2/a (no. 13) |
| Identification | |
| Formula mass | Whiteite-(CaFeMg):756.29g Whiteite-(MnFeMg):767.44g |
| Color | Whiteite-(CaFeMg): Brown, pink-brown or yellow Whiteite-(MnFeMg): Brown |
| Crystal habit | Tabular crystals or aggregates thereof |
| 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 |
| 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][9] |
Whiteite is a rare hydrated hydroxyphosphate mineral.
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),[10] associate curator of minerals at the Smithsonian Institution, and founder, editor and publisher (1970–1982) of the Mineralogical Record.[11]
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.org).
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, US.[7] The type material is conserved at the National School of Mines, Paris, France, and at the National Museum of Natural History, Washington DC, US, 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]
- ^ a b c d e f Gaines et al (1997) Dana's New Mineralogy Eighth Edition. Wiley
- ^ a b c d e f "Whiteite-(CaFeMg) Mineral Data". Webmineral.com. Retrieved 2012-03-15.
- ^ a b c d e "Whiteite-(MnFeMg) Mineral Data". Webmineral.com. Retrieved 2012-03-15.
- ^ a b c d e "Whiteite-(CaMnMg) Mineral Data". Webmineral.com. Retrieved 2012-03-15.
- ^ a b c d e f g h i j k l "Handbook of Mineralogy". Handbook of Mineralogy. Retrieved 2012-03-15.
- ^ 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]
- ^ a b c "Whiteite-(CaFeMg): Whiteite-(CaFeMg) mineral information and data". Mindat.org. 2012-01-30. Retrieved 2012-03-15.
- ^ a b "IMA Mineral List with Database of Mineral Properties". Rruff.info. Retrieved 2012-03-15.
- ^ Elliott, Peter; Willis, Anthony C. (1 March 2019). "Whiteite-(mnmnmg), a New Jahnsite-Group Mineral from Iron Monarch, South Australia: Description and Crystal Structure". The Canadian Mineralogist. 57 (2): 215–223. doi:10.3749/canmin.1800070. S2CID 133690952.
- ^ "Label Archive". The Mineralogical Record. 1933-09-30. Retrieved 2012-03-15.
- ^ "The Mineralogical Record". The Mineralogical Record. Retrieved 2012-03-15.