Sturmanite

Sturmanite is a rare sulfate mineral with the chemical formula Ca6Fe3+2(SO4)2.5(B(OH)4)(OH)12 · 25 H2O.[2][3][4] 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.[5]

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)		Ca6Fe3+2(SO4)2.5[B(OH)4](OH)12 · 25 H2O
IMA symbolStrm[1]
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

Occurrence

Sturmanite was first identified in 1983 and approved by the IMA in the same year.[4][5] 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.[5] 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.[2] It is found as a rare secondary mineral embedded in manganese deposits and is associated with baryte, manganite, hausmannite, and hematite.[3]

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.[6]

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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