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Sturmanite

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Rare sulfate mineral
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
CategorySulfate minerals
Formula
(repeating unit)		Ca6Fe2(SO4)2.5(OH)12 · 25 H2O
IMA symbolStrm
Strunz classification7.DG.15
Dana classification32.4.4.2
Crystal systemTrigonal
Crystal class3m - Ditrigonal Pyramidal
Space groupP31c (no. 159)
Unit cella = 11.188(9) Å, c = 21.91(7) Å
Identification
ColorBright yellow to amber
Crystal habitHexagonal, pyramidal, prismatic
CleavagePerfect {1010}
TenacityBrittle
Mohs scale hardness2.5
LusterVitreous, greasy
StreakPale yellow, greenish yellow, brownish orange
DiaphaneityTransparent to translucent
Specific gravity1.847 (measured) 1.855 (calculated)
Optical propertiesUniaxial (+/-)
Birefringenceδ = 0.002
Ultraviolet fluorescencenone

Sturmanite is a rare sulfate mineral with the chemical formula Ca6Fe2(SO4)2.5(B(OH)4)(OH)12 · 25 H2O. 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), Croatian-Canadian mineralogist and Curator Emeritus of Mineralogy, Royal Ontario Museum.

Occurrence

Sturmanite was first identified in 1983 and approved by the IMA in the same year. 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. 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. It is found as a rare secondary mineral embedded in manganese deposits and is associated with baryte, manganite, hausmannite, and hematite.

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.

References

  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ "Sturmanite: Sturmanite mineral information and data". www.mindat.org. Retrieved 2017-02-19.
  3. ^ "Sturmanite" (PDF). Handbook of mineralogy.
  4. ^ Barthelmy, Dave. "Sturmanite Mineral Data". www.webmineral.com. Retrieved 2017-02-19.
  5. ^ Peacor, D.R., Dunn, P.J., Duggan, M. (1983). "Sturmanite, a ferric iron, boron analogue of ettringite". Canadian Mineralogist. 21: 705–709.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  6. 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 (3): 723–729. CiteSeerX 10.1.1.605.4915. doi:10.2113/gscanmin.42.3.723.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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