Chap. IV. ] 
WAD. 
117 
The characters as given by Dana are as follows : — 
' In amorphous and reiiifomi masses, either earthy or compact • also 
incnisting or as stains. Usually very soft, soihug the fingers : less often 
hard to H. =6. G. =3 0 - 4*26 ; often loosely aggregated, and feeling very 
light to the hand. Colour dull black, bluish or brownish black.' 
There seems, however, to be everv passage between psilomelane ani 
wad, so that one often finds a specimen that ono is doubtful whether to 
call psilomelane or wad. 
In naming Indian specimens of manganeso-ores, the practice I have 
followed with regard to the imcrvstallized or amorphous ores is to 
designate all those as psilomelane that in any w^ij exhibit the characters 
of that mineral, the hardness especially being a criterion. If the mineral 
be a soft one, and show a finely crystalline structiire, I have relegated it to 
pyrolusite, whilst if it show no signs of crystalUne structure nor of the 
compact, firm amorphous structure of psilomelane, I have called it wad, 
this term being thus reserved for the indefinite mixtures so often found 
in manganese- ore deposits i. 
Some ot the chief localities for wad are the various deposits in the 
Vizagapatam district, where this substance has 
^)ccuw^hcg 
often been formed in considerable quantities by 
the replacement of the lithomargic matter accompanying the ore deposits. 
Wad is also extremely abvmdant in association with the manganese-ore 
deposits of the Sandur Hills and Mysore State. In the Sandur HUls it is 
best exposed in the deposits being worked at Raraandrug. Here it is 
intimately associated with psilomelane, the two together torming a very 
considerable proportion of the ores extracted. It is evndent from the mode 
of association of these two minerals that the wad is the first- formed 
mineral and that it subsequently gets converted into the psilomelane, pro- 
bably on the advent of a further portion of manganese in solution. The 
wad itself tends to be tabular or laminated in form^ owing to its having 
been formed by the replacement of original laminated rocks, probably 
slates or phyllites. In colour it is greyish black, giving a soap-like 
atreak that varies in colour from deep chocolate through brownish 
black to nearly black. It is fairly compact, but very soft, and usually 
preserves the original slaty or phyllitic structure of the rock that 
1 M. Gorgeu, in his paper ■ Sur les oxydes dc manganese naturels '. Bull, de la 
Soc fr- de Mineralogique, III, pp. 25 — 28, (1890), regards wads or " manganese liege ' 
as true manganites. acid and hj-drated. and conforu'ing in certain cases to tbe 
formulae : — 
3{Mna2)RO.H20 and 3(Mn02)R0.3H20. 
He also says that wads are sometimes erystalline. 
