Poldervaartite (very closely related to Olmiite)
Current inventory:  0 gems
 

  
Poldervaartite was named to honor Arie Poldervaart (1918 - 1964), who was a Professor of Petrology at Columbia University, New York City, New York, USA.

Discovered in 1992; IMA status: Valid (Approved 1993)

Chemistry

Chemical Formula:

(CaMn²⁺)₂(SiO₃OH)(OH)

Calcium Manganese Silicate Hydroxide

Molecular Weight:

197.68 gm

Composition:

Calcium

30.41 %

Ca

42.55 %

CaO

Manganese

13.90 %

Mn

17.94 %

MnO

Silicon

14.21 %

Si

30.39 %

SiO₂

Hydrogen

1.02 %

H

9.11 %

H₂O

Oxygen

40.47 %

O

Classification

Mineral Classification:

Silicates (Germanates)

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. The Ca-dominant analogue of Olmiite.

Varieties:

None

Synonyms:

IMA1992-012

Crystal Data

Crystallography:

Orthorhombic - Dipyramidal

Crystal Habit:

Crystals are prismatic, with {110}, {100}, {010}, and {001}, to 7 mm; aggregates in sheaves.

Twinning:

None

Physical Properties

Cleavage:

None observed

Fracture:

Irregular/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, milky white, pink-white

Transparency:

Transparent, Translucent

Luster:

Vitreous on fractures to Sub-Vitreous on crystal faces

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, Hausmannite, Henritermierite, Bultfonteinite, Hematite, Calcite

Common Impurities:

Fe, Mg, H₂O

Type Locality:

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

Year Discovered:

1992; (IMA approved 1993)

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 at 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 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.
 

  
Poldervaartite gems for sale (please see our Olmiite gems for sale)