1) Trigonal mineral 
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. It was named after Edward Sydney Simpson (1875–1939), government mineralogist and analyst of Western Australia. It is an a...