56 
MANGANESE-ORE DEPOSITS OF INDIA : MINERALOGY. [PaRT I 
70° 21', Now the following values for tMs angle pp' have been deter- 
mined by various observers : — 
Author. 
Locality. 
Value. 
Haidinger 1 . . . 
St. Marcel, Piedmont 
70^ 7' 
Des Cloizeaux 2 . 
Ditto 
70° 14' 
Vom Rath 3 
Ditto 
70° 8' and 70° 13' 
Flink* .... 
Langban, Sweden . 
70° 19' 
It will be seen that the mean of my determinations agrees with 
Fl ink's value rather than those of other observers ; and as the difference 
from that of Flink is only 2', I shall accept his value for the present. I 
do not, however, think that the determinations of the other observers 
are to be regarded as incorrect ; indeed I think it probable that there is a 
small variation in the value of this angle from crystal to crystal, corre- 
sponding with the variation in composition to be noted later ; and pro- 
bably the difference betweim the values of this angle on the Kajlidongri 
and Kacharwahi braunites and on the foreign braunites is due to some . 
difference between the composition of the crystals from the different 
places. It is further probable that even at one locality there is a variation 
from specimen to specimen. Thus of the crystals from Kajlidongri one 
gave the following four values for :— 70° 27', 27^', 26', and 17', the 
images for the first three angles being very good and one of those for the 
fourth edge poor ; whilst another crystal from the same mine gave 
the following values, of which the first three are from very good reflec- 
tions :— 70° 18', 181', 18', and 20|'. Hence it seems probable that the 
composition of these two specimens must be slightly different, corre- 
sponding to an angle of 70° 27' in one case and 70° 18' in the other. 
From the value 70° 19' Flink calculates the value 
cal^axfs^V^ ^'^'■ti- of f, the vertical crystallographic axis, to be 0-9924, 
in the paper cited above, and 0*99218 in a later 
paper. 5 From this value 70° 19', however, I calculate the value to 
be 0-99220, giving the value for c2, so useful in calculating the angles 
between the faces of the crystals, as 0-98447. 
The habits of the crystals from the different localities vary consider - 
1 Trans. Roy. Soc. Edinh., XI, pp. 132-134, (1831). 
2 Annales des Mines, imo. Ser., I, p. 423, (1842). 
^ Silzungsb.d.nied. Gesells. Bonn, p. 224, Dec. 1882. 
« liihung. k. 8v. Vet. Aknd. llandl., XIII, Part II, No. 7, p. 37, (1888). 
» Op. cif., XVI, Part II, No. 4, ,,. 7, (1890). 
