Chap. IV. J 
ANKERITE. 
121 
plete incorporation of the manganates one with another. I have seen 
many exaniples of ores indicating that psilomelane may sometimes pass 
through the stage of loose aggregation characteristic of wad, and later 
become consolidated, perhaps through a more complete union of the 
oxides, with the formation of manganates. The characters of the two 
specimens of wad of which the analyses are given above are shown below. 
A. 221. — Garbhdm. 
This ore is dark grey-brown, and is lithomargic in aspect, being fine- 
grained and fairly adherent when dry. It is very soft (H = about 1) and 
has a dark brown streak. It is dull, except for little patches having 
somewhat of the lustre of graphite and possibly consisting of stained 
kaolinic films. 
A. SSS.—Kodur. 
This shows slickensided surfaces of a shining black colour. It some 
what resembles dirty coal, is more friable than A. 221, and has a nearly 
dead black streak. H=l. Both this and the preceding are light in 
weight, but are too friable for the specific gravity to be determined. 
Aukerite. 
Ankerite is a sub-species of rhombohedral carbonate, intermediate 
in composition between calcite magnesite and siderite ; it has the chemi- 
cal formula CaCO^. (Mg,Fe,Mn)C03. As the formula shows, it also con- 
tains a small quantity of manganese. Amongst the serpentinous crys- 
talline limestones exposed in a nala near Gowari "vV'arhona in the Chhind- 
wara district, and of which an example is described in a paper on the 
petrology of this part of the district^, I found one, 17-68 in the rock- 
register showing reddish brown plates of a rhombohedral carbonate 
enclosing, in a poikilitic fashion, rounded grains of calcite. The dark 
carbonate gives a faint reaction for manganese, and hence is probably to 
be regarded as ankerite ; for it is doubtless also magnesian, since these 
serpentinous limestones almost invariably contain dolomite. 
1 Bee. Geol. Svr. Ind., XXXTTI, p. 202, (1906). 
