Chap. IV. ] 
PSILOMELANE, 
107 
is beautifully conchoidal. The hardness is 6"5, and the specific gravity, 
determined on the above 6 grammes, 3*85, the mineral exhibiting no 
appreciable porosity. 
A. 380. — Tekrasai. 
This specimen I extracted from in situ in a pit at Tekrasai in the Singh- 
bhum district, Bengal, the ore being only about 2 feet below the surface 
of the ground. In colour it is a dark bluish grey, the lustre being quite 
dull except for a few scattered specks that suggest the possible existence 
in the ore of a small quantity of the crystalline manganate, hollandite. 
In structure the ore is minutely pisolitic, on account of which there are 
often, between the separate concretions, minute cavities, which sometimes 
contain a dark brownish black powder, and sometimes are empty. The 
proportion of material different to the main mass of the ore, which may 
be described as a dull dark grey variety of psilomelane, is, however, very 
smaU and will not have affected the analysis to any large extent. In 
consequence of this structure, however, the ore is markedly porous, 
and in taking its specific gravity some day's soaking were found to be 
necessary before the weight in water became constant^. The specific 
gravity was found to be 4"54:. The hardness of the specimen is just 
under 6, and the fracture fairly even, but not conchoidal, the texture not 
being of the requisite fineness for this. The streak is nearly dead black, 
there being a slight brown tinge. 
A. 381 —Tekrasai. 
This specimen was found in situ in the same pit as the preceding one. 
It is the most fine-grained variety I have yet seen, having more the texture 
of porcelain than of anything else. It is not, however, hard, but is easily 
scratched by fluorite and has a hardness of about 3 ; one of the most 
interesting features about it is the fact that its fracture surfaces are 
covered with a sort of black bloom that soils the fingers in the same way 
as the bloom on a plum does. When this bloom is on, the colour can best 
be described as a dull iron-black, with perhaps just a tinge of brown. 
If, however, this bloom be rubbed off with the finger, as it easily can be, 
the mineral is seen to be a shining iron-black with perhaps a tinge of 
brown in it. The lustre is perhaps best described as resinous, when the 
1 In all cases the specimens were afterwards dried by putting them outside on ths 
top of an airbath so as to remove, before powdering for analysis, the water absorbed 
during the determination of the specific gravity. 
