Data for some African columbite-tantalite specimens

The degree of order is discussed according to the a 0 /c 0 ratio. Five originally disordered specimens (a0/c0 = 2 . 7 6 9 — 2 . 8 1 1 ) and ones original ly ordered specimen (a0/c0 = 2 .832) were heated at 1 ,000° C f o r one hour. A s a result the a 0 /c 0 ratio in the disordered specimens increased to 2.829—2.833, causing the specimens to become ordered and the originally ordered specimen's a 0 /c 0 ratio decreased to 2 .7 8 8. Three X r a y dif fractograms are presented [based on the averages o f all d i f f ractograms, and differences in: 1) disordered columbite or tantalite ( 1 1 0 peak may or may not be present, but when it is, it is very weak), 2) ordered Mn-tantalite ( 110 , 200, 400, 600, and 023 peaks are primarily much stronger than in columbite or tantalite and the 7 1 1 + 512 , 42 1 , and 1 1 2 is present in Mn-tantalite but not in columbite or tantalite) and 3) disordered structures transformed into ordered structures (200, 400, 600, and 023 peaks have become more prominent, the 421 , 7 1 1 f 5 1 2 are n o w present, and the 1 1 2 is not present]. Chemical analyses of some 108 columbite-tantalite specimens (including the specimens examined in this paper) are plotted according to their end members. The specimens approaching the Mn-tantal i te end member are well represented.