What is "simpsonite"

n. (context mineralogy English) A trigonal-pyramidal mineral containing aluminum, hydrogen, niobium, oxygen, and tantalum.

Simpsonite has a general formula of Al(Ta,Nb)O(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 Paraiba mines of Rio Grande do Norte, Brazil and at Tabba Tabba, Western Australia.