thaumasite, rectangular step cut - South Africa
thaumasite, rectangular step cut - South Africa

Thaumasite Value, Price, and Jewelry Information


For a long time, rare thaumasite crystals — pale, fragile, and with little to no fire — were interesting primarily as mineral specimens. With the discovery of even rarer facetable material, cut thaumasites are now prized collector’s gems.

2 Minute Read

For a long time, rare thaumasite crystals — pale, fragile, and with little to no fire — were interesting primarily as mineral specimens. With the discovery of even rarer facetable material, cut thaumasites are now prized collector’s gems.

thaumasite, rectangular step cut - South Africa
Colorless 0.35-ct thaumasite, rectangular step cut, 5.4 x 4 mm, South Africa. © The Gem Trader. Used with permission.
thaumasite crystals - South Africa
Thaumasites on matrix, 3.1 x 2.1 x 1.9 cm, N'Chwaning II Mine, Kalahari Fields, Northern Cape Province, South Africa. © Rob Lavinsky, www.iRocks.com. Used with permission.

What is Thaumasite?

Thaumasite belongs to the ettringite mineral group. None of these minerals appear commonly in jewelry, but thaumasites and ettringites themselves are the most likely to be faceted.

Does Thaumasite Make a Good Jewelry Stone?

You're more likely to find cut thaumasites in rare gem collections than jewelry collections. They have a hardness of only 3.5, which makes them very susceptible to scratching. (However, they seem to harden after exposure to air). Combined with their lack of dispersion, they just don't make very practical or desirable jewelry stones. Any thaumasite in jewelry should have a protective setting and is best reserved for occasional wear.

Prior to the discovery of facetable material in South Africa in the 1980s, gem cutters sometimes cut cabochons from compact, massive thaumasite. Some of these cabs show an interesting but relatively weak cat's eye effect.

Identifying Thaumasites

Thaumasite has a very low specific gravity (SG) of 1.91. Thus, it will always feel light for its size.  An SG test should eliminate most possible misidentifications. However, some other rarely encountered gems with low SG and hardness values as well as similar color ranges include ettringite, gaylussite, inderitekurnakovite, and ulexite. Of these gems, ulexite is probably the most frequently encountered in jewelry or gem collections. 

Thaumasite has high enough birefringence that some cut gems may show facet doubling.

  • thaumasite rough and cut set - South Africa
  • thaumasite, cut corner rectangle - South Africa

    Thaumasite rough and cut set, 0.7 x 0.4 x 0.4 cm (crystal), 1.11 cts, 9.67 mm x 5.08 mm, cut corner rectangle (gem), N'Chwaning Mines, Kuruman, Kalahari manganese field, Northern Cape Province, South Africa. © Rob Lavinsky, www.iRocks.com. Used with permission.

    Are There Any Synthetic Thaumasites?

    Scientists have synthesized both thaumasite and ettringite for research into a form of cement deterioration. However, there's no known jewelry use for this lab-created material.

    There are no known gem enhancements for thaumasites.

    Where is Thaumasite Found?

    To date, the only facetable thaumasite comes from the Kalahari manganese field in Northern Cape Province, South Africa.

    Other notable sources include the following:

    • United States: Cochise County, Arizona; Crestmore, California; Paterson, New Jersey (fine crystals); Centreville, Virginia (in masses); Beaver County, Utah.
    • Långban, Sweden.
    Thaumasite - New Jersey
    Thaumasite: Patterson, New Jersey (specimen around 1 inch across). Photo © Joel E. Arem, PhD, FGA. Used with permission.

    Stone Sizes

    Found as relatively compact fibrous masses up to a few inches in size.

    How to Care for Thaumasites

    Store any thaumasites separately from other harder gemstones to prevent contact scratches. Clean them only with a soft brush, mild detergent, and warm water. For care recommendations, consult our gemstone jewelry cleaning guide.


    Joel E. Arem, Ph.D., FGA

    Dr. Joel E. Arem has more than 60 years of experience in the world of gems and minerals. After obtaining his Ph.D. in Mineralogy from Harvard University, he has published numerous books that are still among the most widely used references and guidebooks on crystals, gems and minerals in the world.

    Co-founder and President of numerous organizations, Dr. Arem has enjoyed a lifelong career in mineralogy and gemology. He has been a Smithsonian scientist and Curator, a consultant to many well-known companies and institutions, and a prolific author and speaker. Although his main activities have been as a gem cutter and dealer, his focus has always been education. joelarem.com


    International Gem Society

    Never Stop Learning

    When you join the IGS community, you get trusted diamond & gemstone information when you need it.

    Become a Member

    Get Gemology Insights

    Get started with the International Gem Society’s free guide to gemstone identification. Join our weekly newsletter & get a free copy of the Gem ID Checklist!