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.
| Simpsonite | |
|---|---|
 Locality: Alto do Giz pegmatite, Rio Grande do Norte, Brazil. Size: 1.6 × 1.5 × 1.8 cm. | |
| General | |
| Category | Oxide minerals |
| Formula (repeating unit) | Al4(Ta,Nb)3O13(OH) |
| IMA symbol | Spn[1] |
| 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 | [2][3][4][5] |
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 Paraíba mines of Rio Grande do Norte, Brazil and at Tabba Tabba, Western Australia.[2]
References
edit- ^ 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.
- ^ a b c Handbook of Mineralogy
- ^ Webmineral data
- ^ a b 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
