Simpsonite
Simpsonite | |
---|---|
![]() Locality: Alto do Giz pegmatite, Rio Grande do Norte, Brazil. Size: 1.6 x 1.5 x 1.8 cm. | |
General | |
Category | Oxide minerals |
Formula (repeating unit) | Al4(Ta,Nb)3O13(OH) |
Strunz classification | 4.DC.10 |
Crystal system | Trigonal |
Crystal class | Pyramidal (3) H-M symbol: (3) |
Space group | P3 |
Unit cell | a = 7.37, c = 4.51 [Å]; Z = 1 |
Identification | |
Formula mass | 813.65 g/mol |
Color | White to cream, yellow to yellow-brown when altered |
Crystal habit | Euhedral, prismatic, striated |
Cleavage | None |
Fracture | Conchoidal |
Tenacity | Brittle |
Mohs scale hardness | 7-7.5 |
Luster | Vitreous to adamantine |
Streak | White |
Diaphaneity | Semitransparent |
Specific gravity | 6.7 |
Optical properties | Uniaxial negative |
Refractive index | nω = 2.045 nε = 2.025 |
Birefringence | δ = 0.020 |
Other characteristics | Blue-white cathodoluminescence and yellow fluorescence in SW UV |
References | [1][2][3][4] |
Simpsonite has a general formula of Al4(Ta,Nb)3O13(OH). It occurs as euhedral to subhedral tabular to short and prismatic crystals, commonly in subparallel groups. Under the petrographic microscope it has a very high relief.
Discovered in 1938, it was named after Edward Sydney Simpson (1875–1939), government mineralogist and analyst of Western Australia.[3] It is an accessory mineral in some tantalum-rich granite pegmatites. It occurs in association with tantalite, manganotantalite, microlite, tapiolite, beryl, spodumene, montebrasite, pollucite, petalite, eucryptite, tourmaline, muscovite and quartz.[1] It is found in a few locations around the world, notably in the Onca and Paraiba mines of Rio Grande do Norte, Brazil and at Tabba Tabba, Western Australia.[1]
References
- ^ a b c Handbook of Mineralogy
- ^ Webmineral data
- ^ a b Simpsonite: Mindat.org
- ^ Philonen, P.C., Grew, E.S., Ercit, T.S., Roberts, A.C., Jambor, J.L. (2005) New mineral names. American Mineralogist, 90, 1227-1233
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