132 W. J. Comstock—Analyses of some American Tantalates. 
sary aid from Professor O. D. Allen. In other respects the 
methods recommended by H. Rose were followed. The ordi- 
nary methods of testing for and separating tin, tungsten cab 
titanium were applied in each case, with negative results. 
The relation between the specific g gravities of columbites and 
tantalites and the percentage of tantalic acid, shown by Marig- 
nac, holds good in these examples also, as will be seen by ¢ a 
comparison with the numbers given in Marignac’s table.* 
Sp. gr. TazOs. 
1. Columbite, Greenland, 5°36 3°3 % 
2. si pi «eee eee 5°65 15°8 
3 e La Valate, near r Limoges, ~ 5-70 13°8 
4, " Bodenmais, (Dianite), .---- 5°74 13°4 
5. zi Haddam, Conn. Decca ett tds 5°85 10-(?) 
6. * Bodenmais, ......---.--- 5°92 27-1 
7 a Haddam, 6°05 30°4 
8 a Bogenmais. ooo lse So 6°06 35-4 
i Haddam, 6°13 31°5 
10. 7-03 65°6 
To wh a are Ge added— 
Sp. gr. Ta2Os. 
sent Co., N.C 6°88 59°92 
rthfield, ‘Made: mt 6°84. 56°90 
Sreich alle Conn 6°59 52°29 
These all agree with the formula (Fe,Mn)(Ta,Nb),O 
Since tantalum and niobium appear capable of replacing 
each other in all proportions in columbites and tantalites, Ram- 
melsberg}+ has suggested that when the number of tantalum 
atoms exceeds that of the niobium atoms, the mineral Bete 
be called tantalite, and when the number of niobium atom 
exceeds that of the tantalum, the mineral should be called es 
lumbite (Rammelsberg uses niobite). According to this method 
of classification, the Yancey county and Northfield minerals 
would be called tantalite, although the latter in form is not to 
oe distinguished from columbite. The manganese niobo- tantal- 
e from Bran chville, “hewerth. Das the ratio ND: la Ae 
ville mineral, and is doubtless the cause of its slight trans- 
lucency and the light color of its powder. 
It is perhaps of interest to add here that a mineral of this 
group from Uté, Sweden, containing 85°5 ae cent of tantalic 
and niobic acids and 95 per cent of m anganese protoxide 
(3°6 FeO), has been called a antantaiatia a Nordenskiéld.t 
* Given in his paper first referred i in which he explains the variations from 
a regular progression, which are seen le. 
+ Mineral Chemie, 2d edition, 1875, in 356. + Zeitsch. Kryst., i, p. 386, 1877. 
