Chap. VIII. ] 
COLUMBITE. 
203 
by Dana amongst the titanosilicates. The composition of the Indian 
mineral as analysed by Damour is shoAvn below : — 
Si02 19 03 
Ti02 20-86 
Ce203 38-38 
AI2O3 7-72 
FeO 7-96 
MnO 0-38 
MgO . 0-27 
CaO ....... 4-40 
H2O and volatile matter . . . . 1' 30 
100-30 
Langier's analysis showed 120% of oxide of manganese, probablv 
Mn304. The specimens from the Urals show 0-75 to 0-83% MnO. 
According to Des Cloiseaux,! the Indian 
' matieren est pasparfaitenient liomogene. car j'ai recuniiu au microscope qu ells 
^e compose d'une masse brune sans aucune action .sur la lumiere polarisee, dane 
laquelle sont enchasses de tres-petits grains incolores fortement birefringents'. 
The characters of the Indian mineral are as follows : — H. = 5-5 — 6. 
G. = 4-26. Lustre vitreous, inclining to rednous ; colour brownish 
black, translucent. 
' Tschewkenite ' is also recorded as having been found by the 
Rev. C. F. Muzzy 2 near Dindigul, ' forming a constituent part of por- 
phyritic granite '. But the mineral has never been found since, and 
it is doubtful if the identification was correct. 
Columbite. 
Columbite and tantalite are two related minerals, the former being 
theoretically a niobate or columbate of iron and manganese and the 
latter a tantalate of the same two metals, the theoretical formulae being 
(Fe,Mn)Nb20e and (Fe,Mn)Ta20g, respectively. In Nature minerals 
corresponding to the foregoing formulae are very rarely found, there 
being every gradation from columbite to tantalite by the replacement 
of niobium by tantalum, so that the more general formula is (Fe,Mn) 
(Nb,Ta)206. With an increase in the amount of tantalum and a corre- 
sponding decrease in the amount of niobium in the mineral there is a 
continuous increase in the specific gravity, so that by determining this 
constant it is possible to decide whether to call a particular specimen 
i • Mannel de Mineralogie ', I, p. 554, (1862). 
- '^'atal. Govt. Central Museum, Madras : ' Madura, its rocks and minerals p. 9, 
(18-..}): 
J. H. Nelson. ' The Madura Country ', i-. 15. (1868). 
