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Olmiite  (very closely related to Poldervaartite)
Current inventory:  1 gem
 

Chemistry:  CaMn²⁺[SiO₃(OH)](OH)

Discovered in 2006;   IMA status: Valid (Approved 2006).
Olmiite is named in honor of Filippo Olmi (~ - 2006) of CNR Istituto di Geoscienze e Georisorse sez di Firenze, Florence, Italy for his work in electron microprobe analysis.

Classification

Mineral Classification:

Silicates

Strunz 8th Ed. ID:

8/B.22-25

Nickel-Strunz 10th Ed. ID:

9.AF.90

9 : SILICATES (Germanates)
A : Nesosilicates
F : Nesosilicates with additional anions; cations in [4], [5] and/or only [6] coordination

Related to:

Olmiite - Poldervaartite Series. The Mn2+ dominant analogue of Poldervaartite.

Crystal Data

Crystallography:

Orthorhombic - Dipyramidal

Crystal Habit:

Crystals are prismatic, to 7 mm; aggregates in sheaves.

Twinning:

None

Physical Properties

Cleavage:

None Observed

Fracture:

Irregular to Uneven

Tenacity:

Brittle

Moh's Hardness:

5.0 - 5.5

Density:

3.102 (g/cm³)

Luminescence:

Fluoresces deep red under SW UV

Radioactivity:

Not Radioactive

Optical Properties

Color:

Colorless, White, Pink, Orangish Pink

Transparency:

Transparent to Translucent

Luster:

Vitreous (glassy)

Refractive Index:

1.663 - 1.694  Biaxial ( + )

Birefringence:

0.0310

Dispersion:

Distinct; r > v

Pleochroism:

None

Occurances

Geological Setting:

A product of hydrothermal alteration.

Common Associations:

Bultfonteinite, Celestine, Hematite, Poldervaartite, Sturmanite

Common Impurities:

Fe, Mg, H₂O

Type Locality:

N'Chwaning II Mine, N'Chwaning Mines, Kalahari manganese fields, Northern Cape Province, South Africa

Year Discovered:

2006

View mineral photos:

Olmiite Mineral Photos and Locations

More Information

Mindat.org

Olmiite is a very rare mineral that was discovered in 2006 at the N'Chwaning II Mine, Kalahari manganese fields, Northern Cape Province, South Africa. Wessels Mine and N'Chwaning Mine, both of the Kalahari manganese fields, are still the only known sources of Olmiite. It is a very rare gem because most crystals or not suitable for faceting.  It ranges in color from colorless to light pink. (photograph above courtesy of Jay Medici, gem in picture also faceted by Jay Medici).

It has recently been determined that most Poldervaartite mineral specimens and gems are actually the mineral Olmiite. The two are very closely related, being differentiated only by the percentage of Calcium (Ca) versus Manganese (Mn) contained. Specimens with Mn dominance are Olmiites and those with Ca dominance are Poldervaartites. This would mean that most, if not all, Poldervaartite specimens and gems currently on the market are, in fact, Olmiites. It is impossible to determine the difference between the two visually and must be tested by electron microprobe analysis.

This new information means most, if not all, Poldervaartite gems are actually Ollmiite and that Poldervaartite gems are extremely rare and there may not even be any Poldervaartite gems in existance!
 

  
Olmiite gems for sale: