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.