Simpsonite

{{Infobox mineral

| name = Simpsonite

| category = Oxide minerals

| boxwidth =

| boxbgcolor =

| image = Simpsonite-154999.jpg

| imagesize = 300px

| caption = Locality: Alto do Giz pegmatite, Rio Grande do Norte, Brazil. Size: 1.6 × 1.5 × 1.8 cm.

| formula = {{chem2|Al4(Ta,Nb)3O13(OH)}}

| IMAsymbol = Spn{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}

| molweight = 813.65 g/mol

| strunz = 4.DC.10

| system = Trigonal

| class = Pyramidal (3)
H-M symbol: (3)

| symmetry = P3

| unit cell = a = 7.37, c = 4.51 [Å]; Z = 1

| color = White to cream, yellow to yellow-brown when altered

| habit = Euhedral, prismatic, striated

| twinning =

| cleavage = None

| fracture = Conchoidal

| tenacity = Brittle

| mohs = 7–7.5

| luster = Vitreous to adamantine

| refractive = n_ω = 2.045 n_ε = 2.025

| opticalprop = Uniaxial negative

| birefringence = δ = 0.020

| pleochroism =

| streak = White

| gravity = 6.7

| density =

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| diaphaneity = Semitransparent

| other = Blue-white cathodoluminescence and yellow fluorescence in SW UV

| references = [http://rruff.geo.arizona.edu/doclib/hom/simpsonite.pdf Handbook of Mineralogy][http://www.webmineral.com/data/Simpsonite.shtml Webmineral data][http://www.mindat.org/min-3670.html 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

}}

Simpsonite has a general formula of {{chem2|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.