Sturmanite is a rare sulfate mineral with the chemical formula Ca₆ Fe³⁺₂( SO₄)_2.5( B(OH)₄)( OH)₁₂ · 25 H₂O. It crystallises in the

tetragonal system In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a squar ...

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 The Royal Ontario Museum (ROM) is a museum of art, world culture and natural history in Toronto, Ontario, Canada. It is one of the largest museums in North America and the largest in Canada. It attracts more than one million visitors every year ...

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 The Black Rock mine is a mine located at Hotazel (John Taolo Gaetsewe District Municipality) in the Northern Cape The Northern Cape is the largest and most sparsely populated province of South Africa. It was created in 1994 when the Cape Provi ...

, Black Rock, Kalahari manganese field, Northern Cape Province, South Africa. It is found as flattened dipyramidal crystals on

hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...

and

baryte Baryte, barite or barytes ( or ) is a mineral consisting of barium sulfate ( Ba S O4). Baryte is generally white or colorless, and is the main source of the element barium. The ''baryte group'' consists of baryte, celestine (strontium sulfate), ...

. 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

, manganite, hausmannite, and

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

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