Simpsonite
Locality: Alto do Giz pegmatite, Rio Grande do Norte, Brazil. Size: 1.6 x 1.5 x 1.8 cm.
General
CategoryOxide minerals
Formula
(repeating unit)		Al4(Ta,Nb)3O13(OH)
IMA symbolSpn[1]
Strunz classification4.DC.10
Crystal systemTrigonal
Crystal classPyramidal (3)
H-M symbol: (3)
Space groupP3
Unit cella = 7.37, c = 4.51 [Å]; Z = 1
Identification
Formula mass813.65 g/mol
ColorWhite to cream, yellow to yellow-brown when altered
Crystal habitEuhedral, prismatic, striated
CleavageNone
FractureConchoidal
TenacityBrittle
Mohs scale hardness7-7.5
LusterVitreous to adamantine
StreakWhite
DiaphaneitySemitransparent
Specific gravity6.7
Optical propertiesUniaxial negative
Refractive indexnω = 2.045 nε = 2.025
Birefringenceδ = 0.020
Other characteristicsBlue-white cathodoluminescence and yellow fluorescence in SW UV
References[2][3][4][5]

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.[4] 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.[2] 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.[2]

References

  1. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. 1 2 3 Handbook of Mineralogy
  3. ↑ Webmineral data
  4. 1 2 Simpsonite: Mindat.org
  5. ↑ 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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