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

Chemistry:  (Ca,Mn²⁺)₂(SiO₃OH)(OH)

Discovered in 1992;   IMA status: Valid (Approved 1993).
Poldervaartite was named to honor Arie Poldervaart (1918 - 1964), who was a Professor of Petrology at Columbia University, New York City, New York, USA.

Classification

Mineral Classification:

Silicates

Strunz 8th Ed. ID:

8/B.22-22

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. Thaumasite Series. The Ca-dominant analogue of Olmiite.

Crystal Data

Crystallography:

Orthorhombic - Dipyramidal

Crystal Habit:

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

Twinning:

None

Physical Properties

Cleavage:

None

Fracture:

Irregular to Uneven

Tenacity:

Very Brittle

Moh's Hardness:

5.0

Density:

2.91 (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:

1.634 - 1.656  Biaxial ( + )

Birefringence:

0.0220

Dispersion:

Weak; r < v

Pleochroism:

Weak; X= colorless; Y= light gray; Z= bluish gray

Occurances

Geological Setting:

In a pocket in massive manganese ores in a bedded manganese ore deposit.

Common Associations:

Braunite, Bultfonteinite, Calcite, Hausmannite, Hematite, Henritermierite

Common Impurities:

Fe, Mg, H₂O

Type Locality:

Wessels Mine (Wessel's Mine), Hotazel, Kalahari manganese fields, Northern Cape Province, South Africa

Year Discovered:

1992

View mineral photos:

Poldervaartite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Poldervaartite is an extremely rare mineral that was discovered in 1992 at the Wessels Mine, Hotazel, 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 Poldervaartite. 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 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!
 

  
Poldervaartite (or Olmiite) gems for sale: