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

  1. 1 2 3 Handbook of Mineralogy
  2. ↑ Webmineral data
  3. 1 2 Simpsonite: Mindat.org
  4. ↑ 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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