Simpsonite

Al4(Ta,Nb)3O13(OH)IMA symbolSpn[1]Strunz classification4.DC.10Crystal systemTrigonalCrystal classPyramidal (3)
H-M symbol: (3)Space groupP3Unit cella = 7.37, c = 4.51 [Å]; Z = 1IdentificationFormula mass813.65 g/molColorWhite to cream, yellow to yellow-brown when alteredCrystal habitEuhedral, prismatic, striatedCleavageNoneFractureConchoidalTenacityBrittleMohs scale hardness7–7.5LusterVitreous to adamantineStreakWhiteDiaphaneitySemitransparentSpecific gravity6.7Optical propertiesUniaxial negativeRefractive indexnω = 2.045 nε = 2.025Birefringenceδ = 0.020Other characteristicsBlue-white cathodoluminescence and yellow fluorescence in SW UVReferences[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. ^ a b c Handbook of Mineralogy
  3. ^ Webmineral data
  4. ^ a b 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
Wikimedia Commons has media related to Simpsonite.