THE MINERAL THAUMASITE

  • Chemistry: Ca3Si(CO3)(SO4)(OH)6 - 12H2O, Hydrated Calcium Silicon Carbonate Sulfate Hydroxide.
  • Class: Sulfates
  • Group: Ettringite
  • Uses: Only as mineral specimens.
  • Specimens
Thaumasite is a fairly rare mineral. Its chemistry and classification are interesting. It is sometimes classified as a silicate due to its silicon content and there is an argument to be made for its classification as a carbonate as well. However it does belong to a predominantly sulfate mineral group, the Ettringite Group and its properties seem more in line with its inclusion into the sulfate class.

Four out of every five atoms in this mineral is either a part of a water molecule or an hydroxide. It's almost all water! This fact is reflected in its very low specific gravity of only 1.9, that's less than twice the specific gravity of water.

PHYSICAL CHARACTERISTICS:

  • Color is colorless or white.
  • Luster is vitreous.
  • Transparency: Crystals are translucent.
  • Crystal System is trigonal; bar 3 2/m.
  • Crystal Habits include acicular crystals and massive forms.
  • Cleavage is poor and rarely seen.
  • Fracture is uneven.
  • Hardness is 3.5
  • Specific Gravity is approximately 1.9 (well below average)
  • Streak is white.
  • Associated Mineral is commonly spurrite.
  • Notable Occurrences include Crestmore, Riverside Co., California and Paterson, New Jersey, USA and Langban, Sweden.
  • Best Field Indicators are density, hardness and association.
THAUMASITE specimens:
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THAUMASITE specimen tha-1
$ 120.00
Dims: 0.5 x 0.5 x 0.2" (1.3 x 1.2 x 0.5 cm)
Wt: 1 g w/ foam base
Union, South Africa
A flat cluster of several small Thaumasite crystals makes up this thumbnail specimen. These crystals do not exceed 0.2" (5 mm) in either length or diameter, but are in excellent condition, showing little damage. Their trigonal form is likewise excellent, and occurs in an uncommon prismatic habit. All are colorless, transparent and very clear, and have a vitreous luster. There is no host rock present, and the piece is hot-glued into a plastic thumbnail box.
no photo
tha-1 ($120.00)
Union, South Africa
THAUMASITE specimen tha-2
$ 100.00
Dims: 0.4 x 0.3 x 0.1" (1.0 x 0.7 x 0.4 cm)
Wt: 9 g w/ specimen box
Union, South Africa
Two partly intergrown Thaumasite crystals make up this small thumbnail specimen. These crystals do not exceed 0.4" (1.0 cm) in length and are in excellent condition. Their hexagonal prismatic form is likewise excellent, and apparently unusual. Both have an extremely pale (almost colorless) yellow tinge and a vitreous luster, and are transparent and very clear. There is no host rock present, and they are hot-glued inside a plastic thumbnail box.
no photo
tha-2 ($100.00)
Union, South Africa
THAUMASITE specimen tha-3
$ 80.00
Dims: 0.3 x 0.2 x 0.2" (8 x 6 x 6 mm)
Wt: 1 g w/ foam base
Union, South Africa
A single hexagonal Thaumasite crystal makes up this small thumbnail piece. It is in excellent condition and has excellent hexagonal prismatic form. Though nearly colorless, it does show a faint yellow tinge. It is colorless and transparent and has a vitreous luster. It is unattached to a base or host rock, and is hot-glued into a plastic thumbnail box.
no photo
tha-3 ($ 80.00)
Union, South Africa
 

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