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.
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 pegmatites. It occurs in association with tantalite, tapiolite , montebrasite, eucryptite and quartz It is found in a few locations around the world, notably in the Onca and Paraiba mines of Rio Grande do Norte and at Tabba Tabba