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Thomsonite-Ca
Current inventory:  1 gem
 

   

Thomsonite

Chemistry:  NaCa2Al5Si5O206(H2O)

Discovered in 1820;   IMA status: Valid (pre-IMA; Grandfathered).
Thomsonite is n
amed after Dr. Thomas Thomson (1773-1852) the Scottish chemist and mineralogist who first analyzed the material. The Ca modifier was added by the Zeolite Committee due to its Calcium content.

 

Classification

   

   

Mineral Classification:

Silicates

Strunz 8th Ed. ID:

8/J.21-70

 

8 : Silicates
J : Tectosilicates (network) without anions unfamiliar to the tetraheders
21 : Zeolite group, Natrolite - Thomsonite series

 

 

Crystal Data

   

   

Crystallography:

Orthorhombic - Dipyramidal

Crystal Habit:

Commonly prismatic, acicular, or bladed, flattened, elongated and striated, to 12 cm; in radiated spherical or columnar aggregates; smooth, globular, botryoidal; compact, massive. Twinning: On [110].

 

 

Physical Properties

   

 

Cleavage:

[101] Perfect, [100] Good

Fracture:

Uneven, Conchoidal, Subconchoidal

Tenacity:

Brittle

Moh's Hardness:

5.0 - 5.5

Density:

2.30 - 2.40 (g/cm3)

Radioactivity:

Not Radioactive

 

 

Optical Properties

   

   

Color:

Colorless, White, Greenish, Yellow, Pink; may be concentrically zoned

Transparency:

Transparent to Translucent

Luster:

Vitreous (Glassy), Pearly

Refractive Index:

1.511 - 1.545  Biaxial ( + )

Birefringence:

0.0050 - 0.0150

Dispersion:

Dispersion distinct to strong, r > v

Pleochroism:

Colorless

 

 

Occurances

   

   

Geological Setting:

Found in amygdules and fractures in maffic igneous rocks, typically basalts; in some alkalic igneous rocks, contact metamorphic zones, and hypabyssal rocks. As an authigenic cement in some sandstones.

Type Locality:

Old Kilpatrick, Strathclyde (Dunbartonshire), Scotland, UK

Year Discovered:

1820

View mineral photos:

Thomsonite Mineral Photos and Locations

 

 

More Information

   

   

 

Mindat.org
Webmineral.com

 

 


Thomsonite is a member of the
Zeolite Group of minerals that includes over 40 minerals and these gem-type minerals: Analcime, Barrerite, Chabazite, Epistilbite, Gmelinite-Na, Goosecreekite, Mordenite, Natrolite, Pollucite, Scolecite, Stellerite, Stilbite, Thomsonite and Yugawaralite.

Thomsonite can be found in many locations worldwide but only few produce good crystal specimens and even fewer produce the beautiful and colorful concentric "eye" patterns like those found in the western Lake Superior area; Isle Royal and the Keweenaw Peninsula in Michigan and the Grand Marais, Minnesota area.

Pure Thomsonite is snow-white and sometimes translucent; very, very rarely suitable for faceting. Impurities such as ferric and/or ferrous iron or copper are responsible for the various colorations within the mineral. Commonly found colors are pink, tan, white, red and brown. Those with green, gray or black backgrounds or green eyes are the most highly prized but rarely found. These concentric, colorful eye patters make beautiful cabochons.
 

  
Thomsonite gems for sale:

Thomsonite-001

Gem:

Thomsonite

Stock #:

THOMS-001

Weight:

18.8515 ct

Size:

16.02 x 17.70 x 10.06mm

Shape:

Free-form

Color:

Multi-color

Clarity:

Opaque

Origin:

Western Lake Superior area, USA

Treatment:

None (natural)

Price:

$69.00

Pictures are of the actual gem offered for sale.
Gem images are magnified to show detail.

Thomsonite-001

This Thomsonite shows some beautiful "eyes" and colors.




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