Thaumasite
A variety of Ettringite Group
What is Thaumasite?
Thaumasite is a rare mineral that occurs in the form of translucent or transparent hexagonal crystals. Although very attractive, thaumasite is quite soft and fragile, so you will usually find it cut into cabochons. Its name comes from the Greek word "thaumazein," meaning "to be surprised" or "to wonder," which refers to its unusual chemical compositions.
Etymology & Origins
It was first described in 1878 in Sweden and named from the Greek, "thaumazein", to be surprised, in reference to its unusual composition with carbonate, sulfate and hydroxysilicate anions.
Optical Properties
- Refractive Index
- 1.467-1.505
- Birefringence
- 0.038
- Optical Character
- Uniaxial negative
Market Value Factors
Pricing varies for every rock and mineral, so use these universal factors to gauge Thaumasite before comparing listings or appraisals.
Size & Weight
Larger, intact specimens usually command higher prices.
Rarity & Demand
Scarce material or popular varieties sell at a premium.
Condition & Finish
Chips, repairs, and heavy wear lower value; clean prep helps.
Treatment & Provenance
Untreated specimens with documented locality are prized.
Thaumasite Localities Map
See where Thaumasite is found with a localities map, collecting zones, and geology context. Generate a sample map preview below.
Key Characteristics
Formation of Thaumasite
It occurs as a hydrothermal alteration mineral in sulfide ore deposits and geothermal alteration of basalt and tuff. It occurs with zeolites, apophyllite, analcime, calcite, gypsum and pyrite.
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Quick Facts
Physical Properties
- Color
- Colourless, white
- Hardness (Mohs)
- 3.5
- Density
- 1.88 - 1.9 g/cm³
- Streak
- White
- Luster
- Vitreous
- Crystal System
- Hexagonal
Chemical Properties
- Chemical Formula
- Ca3(SO4)Si(OH)6 · 12H2O
- Elements
- C, Ca, H, O, S, Si
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Thaumasite FAQs
How do I identify Thaumasite?
Thaumasite can be identified by its hardness of 3.5 on the Mohs scale, Colourless color, Vitreous luster, Hexagonal crystal system. Look for these key characteristics when examining specimens.
What color is Thaumasite?
Thaumasite typically appears in Colourless, white. Color can vary depending on impurities and formation conditions.
How hard is Thaumasite?
Thaumasite has a hardness of 3.5 on the Mohs scale. This gives it moderate hardness.
What is the formation of thaumasite of Thaumasite?
It occurs as a hydrothermal alteration mineral in sulfide ore deposits and geothermal alteration of basalt and tuff. It occurs with zeolites, apophyllite, analcime, calcite, gypsum and pyrite.
