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

  
Olmiite was 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.

Discovered in 2006; IMA status: Valid (Approved 2006)

Chemistry

Chemical Formula:

(CaMn²⁺)₂(SiO₃OH)(OH)

Calcium Manganese Silicate Hydroxide

Molecular Weight:

203.44 gm

Composition:

Calcium

22.65 %

Ca

31.70 %

CaO

Manganese

22.95 %

Mn

29.64 %

MnO

Iron

0.27 %

Fe

0.35 %

FeO

Silicon

13.81 %

Si

29.53 %

SiO₂

Hydrogen

0.99 %

H

8.86 %

H₂O

Oxygen

39.32 %

O

100.00 %

100.08 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

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.

Varieties:

None

Synonyms:

IMA2006-026, Olmiit

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/Uneven

Tenacity:

Brittle

Moh's Hardness:

5.0 - 5.5

Density:

3.05 (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

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, 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
Webmineral.com

Olmiite is a rare mineral that was discovered in 2006 at the N'Chwaning II Mine, Kalahari manganese fields, Northern Cape Province, South Africa. The Wessels Mine and N'Chwaning Mines, both in the Kalahari manganese fields, are still the only known sources of Olmiite. It is a rare gem because most crystals or not suitable for faceting.  It ranges in color from colorless to light orangish-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 Olmiite and those with Ca dominance are Poldervaartite. This would mean that most, if not all, Poldervaartite specimens and gems currently on the market are, in fact, Olmiite and that there may not even be any Poldervaartite gems in existance! . It is impossible to determine the difference between the two visually and must be tested by electron microprobe analysis.
 

Olmiite gems for sale: