Chap. III. ] 
BRAUNITE. 
6T 
In all the analyses considered the ratio of m : n lies between the limits 
3 : 1 and 4:1. As manganese is the predominant basic constituent the 
formula can be more definitely stated as — 
m MnMnOa ^ n JlnSiOa- 
On the supposition, which has yet to be proved, that the Si in a 
metasilicate is isomorphous with the Mn in a manganite, this formula 
can be further simplified to — 
■\In(Mn,Si)03. 
The most general ratio of m to n is perhaps 3:1; so that the formula 
of braimite can be conveniently expressed as — 
3j\IniIn03 + 5InSi03. 
In attempting to find out to which of the various formulae proposed 
the Indian braunites correspond I have three analyses to reply upon. 
These are shown below. The specimen A. 345 was obtained fr^m the 
ore heaps at Garividi station of the ore quarried from Garividi deposit, 
where, as is noticed on page 1055, all the ore is of detrital character, the 
ore-body in situ not having yet been uncovered. This quarry, however, 
happens to be the locahty from which the best specimens of braunite 
are to be obtained in the Vizagapatam district. The specimen was 
black and lustrous, showing perfect cleavage and the most brilliant 
reflections from these cleavage faces. It was a portion of one crystal 
showing a cleavage face over 3 inches long. The portion of it broken 
off for analysis weighed 25 grammes, and had a specific gravity of 4' 79. 
This braunite can be taken as typical of that formed chemically in 
the deposits of the kodurite series. The second specimen, No. 1110, was 
obtained by carefully breaking up two or three crystals of the braunite 
occurring in the albite veins at Kacharwahi in the Nagpur district, and 
making sure that there was no albite in the specimen taken for analysis. 
This mineral in outward appearance was identical with the Garividi speci- 
men, showing the same black lustrous cleavage. The weight taken for 
analysis was 2'69 grammes, of a specific gravity of 4" 79. This braimite 
can be taken as typical of that which occurs in veins of igneous origin. 
The third specimen, 16'815, was obtained after a tedious separation, 
carried out by Mr. T. R. Blyth of the Geological Survey of India, 
from a rock composed of this mineral, winchite, calcite, and quartz, 
sent by Mr. H. J. Winch from Kajlidongri in Jhabua State, Central 
India. The product of the separation consisted of a large number 
of tiny grains of a lustrous black mineral that under the microscope 
showed many triangular faces, indicating an octahedral shape for the 
crystals. From the fact that this mineral was found to be decidedly 
I F 2 
