38 
MANGANESE DEPOSITS OF INDIA: MlNER\LOGY. [ PART 
manganese gahnite, the ratio of iron to alumina being 55 : 47. Besides 
iron and alumina it was found to contain a good deal of zinc and rather 
less manganese than zinc, with a trace of lime and magnesia, and a very 
little silica. The specific gravity was foimd to be 3-95 — 4' 17. 
The specimens collected by Mr. Middlemiss show masses of the dys- 
luite up to 5 inches in length. They are very irregular in shape, some- 
times shewing a tendency to the octahedral form characteristic of 
spinels. The immediately associated minerals are white and pink 
felspar, and biotite. The dysluite itself is black, breaking with a sub- 
conchoidal fracture, which when fresh shows a somewhat resinous 
lustre. The mineral scratches quartz. It is very difficult, however, 
to obtain a reaction for manganese in the ordinary way by fusion with 
nitre and fusion mixture. The result of two such tests was to lead to 
the supposition that manganese was not present. On first fusing the 
uiineral with acid potassium sulphate and then adding nitre and fusion 
uiixture a decided manganese reaction was, however, obtained. The 
streak of the mineral is a somewhat darkish grey. 
Manganmagnetite. 
As its name implies mangaimiagnetite is a variety of magnetite con- 
taining manganese. Three localities have been so far recorded for 
this variety. They are : — 
Locality. Contains : — G. 
Vester Silfberg, Swedenl . . 3 80 and 6-27% MnO . . 5-064 
New Zealand2 . . . 4-63% Mn203 and 7-15% MgO 4-67 
Kodur, Vizagapatam, Madras3 . 3-00% Mn304, 2-52% AI2O3 5-045 
There seems to be some doubt as to which portion of the magnetite 
molecule contains the manganese. Thus the general formula of man- 
ganmagnetite may be expressed as (Fe,Mn)0.(Fe,Mn)304 ; or, if allowance 
be made for the magnesia shown in the New Zealand specimen and 
the alumina shown in the Kodur specimen, the formula may be stated 
as follows :— (Fe,Mn,Mg)0.(Fe,Mn,Al)304. And, if the presence of the 
alumina be neglected, manganmagnetite may be looked upon as provid- 
ing the connecting link between magnetite and jacobsite. The Indian 
1 Mats WeihuU, Min. v. jxlr. Mitlheil., VII, j). 109. (1886). 
2 A. H. Ch.-ster, Min. Mwj., VIII, p. 125, (1889). 
3 T. H. Holland, Rec. Oeol. Sur. Ind., XXVI, p. 165. (1893). 
