Sturmanite

{{Short description|Rare sulfate mineral}} {{Infobox mineral|name=Sturmanite|boxwidth=|boxbgcolor=|image=Sturmanite-240577.jpg|imagesize=260px|alt=|caption=Distinctive sturmanite on matrix from the N'Chwaning Mines. Size: 5.4 x 4.2 x 1.7 cm. Ex.Charlie Key Stock|category=Sulfate minerals|formula=Ca₆Fe³⁺₂(SO₄)_2.5[B(OH)₄](OH)₁₂ · 25 H₂O| IMAsymbol = Strm<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3 |pages=291–320|doi=10.1180/mgm.2021.43 |bibcode=2021MinM...85..291W |s2cid=235729616 |doi-access=free}}</ref>|molweight=|strunz=7.DG.15|dana=32.4.4.2 |system=Trigonal |class = 3m - Ditrigonal Pyramidal |symmetry=''P31c'' (no. 159)|unit cell=a = 11.188(9) Å, c = 21.91(7) Å|color=Bright yellow to amber|colour=|habit=Hexagonal, pyramidal, prismatic|twinning=|cleavage=Perfect {1010}|fracture=|tenacity=Brittle|mohs=2.5|luster=Vitreous, greasy|streak=Pale yellow, greenish yellow, brownish orange|diaphaneity=Transparent to translucent|gravity=1.847 (measured)

1.855 (calculated)|density=|polish=|opticalprop=Uniaxial (+/-)|refractive=|birefringence=δ = 0.002|pleochroism=|2V=|dispersion=|extinction=|length fast/slow=|fluorescence=none|absorption=|melt=|fusibility=|diagnostic=|solubility=|impurities=|alteration=|other=|prop1=|prop1text= }} '''Sturmanite''' is a rare sulfate mineral with the chemical formula Ca₆Fe³⁺₂(SO₄)_2.5(B(OH)₄)(OH)₁₂ · 25 H₂O.<ref name=":0" /><ref name=":2" /><ref name=":1" /> 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.<ref name=":3" />

== Occurrence == Sturmanite was first identified in 1983 and approved by the IMA in the same year.<ref name=":1">{{Cite web|url=http://www.webmineral.com/data/Sturmanite.shtml#.WKm2ZjsrK00|title=Sturmanite Mineral Data|last=Barthelmy|first=Dave|website=www.webmineral.com|access-date=2017-02-19}}</ref><ref name=":3">{{Cite journal|last=Peacor, D.R., Dunn, P.J., Duggan, M.|year=1983|title=Sturmanite, a ferric iron, boron analogue of ettringite|url=https://www.researchgate.net/publication/242120069|journal=Canadian Mineralogist|volume=21|pages=705–709}}</ref> 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.<ref name=":3" /> 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.<ref name=":0">{{Cite web|url=https://www.mindat.org/min-3817.html|title=Sturmanite: Sturmanite mineral information and data.|website=www.mindat.org|access-date=2017-02-19}}</ref> It is found as a rare secondary mineral embedded in manganese deposits and is associated with baryte, manganite, hausmannite, and hematite.<ref name=":2">{{Cite web|url=http://www.handbookofmineralogy.com/pdfs/sturmanite.pdf|title=Sturmanite|website=Handbook of mineralogy}}</ref>

== 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.<ref>{{Cite journal|last=Pushcharovsky, D.Y., Lebedeva, Y.S., Zubkova, N.V., Pasero, M., Bellezza, M., Merlino, S., Chukanov, N.V.|year=2004|title=The crystal structure of sturmanite|url=http://rruff.info/doclib/cm/vol42/CM42_723.pdf|journal=The Canadian Mineralogist|volume=42|issue=3|pages=723–729|doi=10.2113/gscanmin.42.3.723|citeseerx=10.1.1.605.4915}}</ref>

== References == {{Reflist}}

Category:Iron(III) minerals Category:Calcium minerals Category:Sulfate minerals Category:Hydroxide minerals Category:Borate minerals Category:Trigonal minerals Category:Minerals in space group 159 Category:Borate sulfates