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Simpsonite

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Simpsonite
Locality: Alto do Giz pegmatite, Rio Grande do Norte, Brazil. Size: 1.6 × 1.5 × 1.8 cm.
General
CategoryOxide minerals
Formula
(repeating unit)		Al4(Ta,Nb)3O13(OH)
IMA symbolSpn
Strunz classification4.DC.10
Crystal systemTrigonal
Crystal classPyramidal (3)
H-M symbol: (3)
Space groupP3
Unit cella = 7.37, c = 4.51 ; 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

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. 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. It is found in a few locations around the world, notably in the Onca and Paraíba mines of Rio Grande do Norte, Brazil and at Tabba Tabba, Western Australia.

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. ^ Handbook of Mineralogy
  3. Webmineral data
  4. ^ 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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