The chemical composition of this mineral group is very variable. The actual
columbite tantalite family consists of the columbite mixed crystal series (with the
end members columbite (Fe) and columbite (Mn)) as well as from the tantalite
solid solution series (with the end members tantalite (Fe) and tantalite (Mn) ).
Between all four end members there is the possibility of solid solution formation,
which however is not complete in certain areas. Occasionally, the antimony-rich
minerals Stibiotantalit and Stibiocolumbit are counted. Primarily attached to
crystalline rocks, inter alia at alkaline pegmatite passages, these minerals are
often found on secondary deposits, such as heavy mineral soaps.