SIMPSONITE: Brazil (0.27). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Simpsonite is an extremely rare gemstone. The material from Western Australia is bright yellow-orange and very beautiful. The mineral is hard and durable, with no cleavage, and could easily become a popular gemstone if it were more abundant. Gems over 1 carat should be considered extremely rare because clean material is a very small percentage of the limited supply of simpsonite that has been found.
| Data | Value |
|---|---|
| Name | Simpsonite |
| Stone Sizes | Crystals have been found up to 5 cm but only tiny stones have been cut from available rough. Ln general, stones are only seen from Brazil and Australia. A typical size is 0.5-1 carat. |
| Formula | Al4Ta3O13(OH). |
| Colors | Colorless, pale yellow, cream white, light brown, orange. |
| Fracture | Conchoidal |
| Hardness | 7-7.5 |
| Cleavage | None |
| Crystallography | Hexagonal. Crystals tabular, prismatic; also in crystalline masses. |
| Refractive Index | 1.976-2.034 |
| Birefringence | 0.058 |
| Luminescence | In SW, bright blue-white (Western Australia), bright pale yellow (Bikita, Zimbabwe), medium pale yellow (Ecuador) or light blue (Paraiba, Brazil). |
| Luminescence Present | Yes |
| Luminescence Type | Fluorescent, UV-Short |
| Absorption Spectrum | Not diagnostic. |
| Pleochroism | None. |
| Optics | o = 2.034; e = 1.976. Uniaxial (-). |
| Optic Sign | Uniaxial - |
| Luster | Vitreous, adamantine. |
| Specific Gravity | 5.92-6.84 |
| Transparency | Transparen to translucent. |
Optics: o= 2.034; e=1.976.
Uniaxial (-).
Occurrence: In granite pegmatites, usually with biotite.
Bikita, Zimbabwe; Alto do Giz, Ecuador; Kola Peninsula, USSR.
Onca and Paraiba, Brazil: facetable material.
Tabba Tabba. Western Australia: facetable yellowish crystals.
Comments: Simpsonite is an extremely rare gemstone. The material from Western Australia is bright yellow-orange and very beautiful. The mineral is hard and durable, with no cleavage, and could easily become a popular gemstone if it were more abundant. Gems over 1 carat should be considered extremely rare because clean material is a very small percentage of the limited supply of simpsonite that has been found.
Name: After Dr. E. S. Simpson, former government mineralogist of Western Australia.
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