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.

Discovered in 1938, it was named after Edward Sydney Simpson (1875–1939), government mineralogist and analyst of Western Australia.

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.