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Thaumasite
Current inventory:  1 gem
 

Chemistry:  Ca₃Si(CO₃)(SO₄)(OH)₆·12(H₂O)

Discovered in 1878;   IMA status: Valid (pre-IMA; Grandfathered).
Thaumasite is named from the Greek word thaumazein meaning surprising in allusion to its rather unusual chemical composition with carbonate, sulphate and hexahydroxysilicate anions.

Classification

Mineral Classification:

Sulfates

Strunz 8th Ed. ID:

8/B.22-90

Nickel-Strunz 10th Ed. ID:

7.DG.15

7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
D : Sulfates (selenates, etc.) with additional anions, with H₂O
G : With large and medium-sized cations; with NO₃, CO₃, B(OH)₄, SiO₄ or IO₃
15 : Ettringite Group

Crystal Data

Crystallography:

Hexagonal - Dipyramidal

Crystal Habit:

Crystals prismatic, to 5 cm; typically acicular, radiating; powdery, compact, massive.

Twinning:

None

Physical Properties

Cleavage:

Poor, Indistinct

Fracture:

Subconchoidal

Tenacity:

Brittle

Moh's Hardness:

3.5

Density:

1.88 - 1.90 (g/cm³)

Radioactivity:

Not Radioactive

Optical Properties

Color:

Colorless, white, pale yellow.

Transparency:

Transparent to Translucent

Luster:

Vitreous, Silky, Greasy

Refractive Index:

1.458 - 1.507  Uniaxial ( - )

Birefringence:

0.0390

Dispersion:

Very Weak to None

Pleochroism:

None

Occurances

Geological Setting:

A very late-stage mineral in some sulfide ore deposits. In contact metamorphic zones and from the reaction of geothermal waters or seawaters with basalts and tuffs.

Type Locality:

Bjelke Mine, Åreskutan, Åre, Jämtland, Sweden

Year Discovered:

1878

View mineral photos:

Thaumasite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Thaumasite is an extremely rare gem and a member of the Ettingite Group of minerals that includes Charlesite, Ettringite, Sturmanite and Thaumasite. It was discovered at the Bjelke Mine, Åreskutan, Åre, Jämtland, Sweden in 1878. It is a soft mineral but seems to harden with exposure to air. Sources of gem quality crystals include Paterson, New Jersey and the Kalahari manganese fields of the Northern Cape Province, South Africa.
 

  
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