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Sturmanite
Current inventory:  0 gems
 

Chemistry:  Ca₆(Fe³⁺,Al,Mn²⁺)₂(SO₄)₂[B(OH)₄](OH)₁₂·25(H₂O)
[Hydrated Calcium Iron Aluminum Manganese Sulfate Tetrahydroxoborate Hydroxide]

Discovered in 1981;   IMA status: Valid (IMA approved 1983).
Sturmanite is named in honor of Bozidar Darko Sturman (1937– ), Canadian mineralogist, Royal Ontario Museum, Toronto, Ontario, Canada.

Classification

Mineral Classification:

Sulfates

Strunz 8th Ed. ID:

6/D.13-50

Nickel-Strunz 10th Ed. ID:

7.DG.15

7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
D : Sulfates (selenates, etc.) with additional anions, with H₂O
G : With large and medium-sized cations; with NO₃, CO₃, B(OH)₄, SiO₄ or IO₃

Related to:

Ettringite Group. Ettringite - Sturmanite Series.

Crystal Data

Crystallography:

Trigonal - Ditrigonal Pyramidal

Crystal Habit:

As dipyramidal tabular to elongated hexagonal crystals, to 40 cm, showing [1010], [1014], [1124], typically in groups, may be in stacked parallel aggregates.

Twinning:

Probably twinned (by analogy to ettringite).

Physical Properties

Cleavage:

[1010] Perfect

Fracture:

n/a

Tenacity:

Brittle

Hardness (Mohs):

2.5

Density:

1.847 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Bright to pale Yellow, Greenish Yellow, Brownish Orange (if altered)

Transparency:

Transparent to Translucent

Luster:

Vitreous, Greasy on fracture surfaces

Refractive Index:

1.499 - 1.505  Uniaxial ( +/- )

Birefringence:

0.0020

Dispersion:

None

Pleochroism:

Weak; O = pale green, E = pale yellowish green

Occurances

Geological Setting:

An uncommon secondary mineral in cavities in metamorphosed bedded manganese deposits.

Common Associations:

Barite, Hausmannite, Hematite, Manganite

Type Locality:

Black Rock Mine, Black Rock, Kalahari manganese fields, Northern Cape Province, South Africa

Year Discovered:

1981; IMA approved 1983

View mineral photos:

Sturmanite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Sturmanite is an extremely rare gem and a member of the Ettingite Group of minerals that includes Charlesite, Ettringite, Sturmanite and Thaumasite. It is difficult to distinguish Ettringite from Sturmanite. Both are members of the Ettringite Group of minerals and have similar crystal habit, density, luster and often have the same bright yellow color. By its chemical composition, Sturmanite is about 46% H₂O; it's almost half water! Sturmanite was only recently discovered in 1981 at the Black Rock Mine in the famed Kalahari manganese fields of South Africa. This region is known for its many rare mineral occurances.

The only sources of Sturmanite are from the Kuruman district, with relatively large crystals in the Wessels and N’Chwaning II mines, Northern Cape Province, South Africa.
 

  
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