Poldervaartite is a rare calcium silicate hydroxide mineral primarily known for its delicate, radiating sprays of acicular crystals. It is most famous for specimens from the Kalahari Manganese Field in South Africa, where it often forms spherical aggregates on host rocks like calcite or hausmannite.
Is this poldervaartite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch poldervaartite with a known reference. Poldervaartite sits at Mohs 5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Poldervaartite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Poldervaartite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, pink, orange, brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: sprays of acicular crystals, spherical aggregates.
Often confused with
Poldervaartite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside poldervaartite
Minerals reported to co-occur with poldervaartite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaCa(SiO₄)(OH)₂
- Mohs hardness
- 5
- Density
- 2.8 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Sprays of Acicular Crystals, Spherical Aggregates
- Cleavage
- Good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Manganese Deposits in Hydrothermal Veins
- Typical price
- $50-500 thumbnail, $200-2000 cabinet
Where rockhounds find poldervaartite
Classic worldwide localities
- Wessels Mine, South Africa
- Kalahari Manganese Field, South Africa
Field-hunting tip
Look in manganese deposits in hydrothermal veins country — that is the host setting where poldervaartite typically forms. If you start seeing calcite, hematite, hausmannite in float, you are in the right ground. Field specimens usually show a sprays of acicular crystals, spherical aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify poldervaartite?+
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What rocks look like poldervaartite?+
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Find poldervaartite on the map
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