Sturmanite

Sturmanite
Distinctive sturmanite on matrix from the N'Chwaning Mines. Size: 5.4 x 4.2 x 1.7 cm. Ex.Charlie Key Stock
General
Category Sulfate minerals
Formula
(repeating unit)		 Ca6Fe3+2(SO4)2.5[B(OH)4](OH)12 · 25 H2O
Strunz classification 7.DG.15
Dana classification 32.4.4.2
Crystal system Tetragonal (3m - Ditrigonal Pyramidal)
Unit cell a = 11.188(9) Å, c = 21.91(7) Å
Identification
Color Bright yellow to amber
Crystal habit Hexagonal, pyramidal, prismatic
Cleavage Perfect {1010}
Tenacity Brittle
Mohs scale hardness 2.5
Luster Vitreous, greasy
Streak Pale yellow, greenish yellow, brownish orange
Diaphaneity Transparent to translucent
Specific gravity

1.847 (measured)

1.855 (calculated)
Optical properties Uniaxial (+/-)
Birefringence δ = 0.002
Ultraviolet fluorescence none

Sturmanite is a rare sulfate mineral with the chemical formula Ca6Fe3+2(SO4)2.5(B(OH)4)(OH)12 · 25 H2O.[1][2][3] It crystallises in the tetragonal system and it has a Moh's hardness of 2.5. Sturmanite has a bright yellow to amber colour and falls in the ettringite group. It was named after Bozidar Darko Sturman (born 1937), Slovenian-Canadian mineralogist and former Associate Curator of Mineralogy, Royal Ontario Museum.[4]

Occurrence

Sturmanite was first identified in 1983 and approved by the IMA in the same year.[3][4] It was first found in the Black Rock Mine, Black Rock, Kalahari manganese field, Northern Cape Province, South Africa. It is found as flattened dipyramidal crystals on hematite and baryte.[4] Sturmanite has also been identified in mines near the Black Rock Mine, such as the Wessel's and Perth mines, in the N'Chwaning mines, and near Lakargi Mountain in Russia.[1] It is found as a rare secondary mineral embedded in manganese deposits and is associated with baryte, manganite, hausmannite, and hematite.[2]

Crystal structure

The crystal structure of sturmanite shows two distinct features: one being columns of iron-octahedra and calcium polyhedra, the other being the SO4− and B(OH)4− tetrahedra surrounding these columns. These two structures are linked together through a dense and complex network of hydrogen bonds.[5]

References

  1. 1 2 "Sturmanite: Sturmanite mineral information and data". www.mindat.org. Retrieved 2017-02-19.
  2. 1 2 "Sturmanite" (PDF). Handbook of mineralogy.
  3. 1 2 Barthelmy, Dave. "Sturmanite Mineral Data". www.webmineral.com. Retrieved 2017-02-19.
  4. 1 2 3 Peacor, D.R., Dunn, P.J., Duggan, M. (1983). "Sturmanite, a ferric iron, boron analogue of ettringite" (PDF). Canadian Mineralogist. 21: 705–709.
  5. ↑ Pushcharovsky, D.Y., Lebedeva, Y.S., Zubkova, N.V., Pasero, M., Bellezza, M., Merlino, S., Chukanov, N.V. (2004). "The crystal structure of sturmanite" (PDF). The Canadian mineralogist. 42: 723–729.
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