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Simpsonite
Current inventory:  1 gem
 

Chemistry:  Al₄(Ta,Nb)₃O₁₃(OH)

Discovered in 1938;   IMA status: Valid (pre-IMA; Grandfathered).
Simpsonite is named after Edward Sydney Simpson (1875-1939), a Western Australian government mineralogist.

Classification

Mineral Classification:

Oxides

Strunz 8th Ed. ID:

4/D.27-20

4 : Oxides & Hydroxides
D : Oxides with metal : oxygen = 1:2 (MO2 and related compounds)
27 : Bahianite - Sosedkoite series

Crystal Data

Crystallography:

Trigonal - Pyramidal

Crystal Habit:

Euhedral to subhedral crystals, tabular to short prismatic, and rarely a few other forms, to 2.4 cm; commonly in subparallel groups.

Physical Properties

Cleavage:

None

Fracture:

Conchoidal

Tenacity:

Brittle

Moh's Hardness:

7.0 - 7.5

Density:

6.68 - 6.82 (g/cm³)

Luminescence:

In SW UV, bright blue-white (Western Australia), bright pale yellow (Bikita, Zimbabwe), medium pale yellow (Ecuador), light blue (Paraiba, Brazil)

Radioactivity:

Not Radioactive

Optical Properties

Color:

Colorless, White, Light yellow, Orange-yellow, Brownish yellow, Light brown

Transparency:

Transparent, Semi-Transparent

Luster:

Vitreous, Adamantine

Refractive Index:

2.025 - 2.045  Uniaxial ( - )

Birefringence:

0.0200

Dispersion:

n/a

Pleochroism:

None

Occurances

Geological Setting:

An uncommon accessory mineral in some tantalum-rich granite pegmatites.

Type Locality:

Tabba Tabba pegmatite, Western Australia, Australia

Year Discovered:

1938

View mineral photos:

Simpsonite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Simpsonite is an extremely rare gem that is very attractive in the bright yellow to yellow-orange colors. It is found in a few locations worldwide but only available in facetable crystals from Onca and Paraiba, Brazil and Tabba Tabba, Western Australia. Gems are usually very small since crystals are small and clean material is a very small percentage of the limited supply of Simsonite that has been found. Most crystals are completely opaque. It is a very durable gem with hardness of 7.5 and no cleavage. It would make a very attractive gem for jewelry if it was more abundant.
 

  
Simpsonite gems for sale: