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SECTION III, 1886. 39:71 TRANS. Roy. Soc. CANADA. 
III.— On the Colouring Matter of Black Tourmalines. 
By E.J. CHAPMAN, PH.D. LL.D. 
(Read May 27, 1886.) 
The subspecies of tourmaline, commonly known as “ Schorl ”, presents a deep-black 
colour, combined with perfect opacity. Typical examples, even in fine splinters and on 
the thinnest edges, are completely opaque. To what is this black, opaque condition due ? 
As shown by numerous analyses, and notably by those of Gmelin, Mitscherlich and 
Rammelsberg, the only glass-colouring elements present in tourmaline are iron and man- 
ganese. Most of the older analyses, as those of Gmelin, as well as the still earlier deter- 
minations of Klaproth and others, assume the iron to be present in the condition of 
ferro-ferric oxide, Fe’ O', and the manganese in that of manganic oxide, Mn° O*. In the 
analyses of Arfvedson and Gruner, made at about the same date as those of Gmelin, both 
metals are regarded as sesquioxides; whilst in the comparatively modern analyses of 
Mitscherlich and Rammelsberg they are asserted to be present as monoxides (Fe O and 
Mn O). The facts and deductions brought forward in this attempt to trace out the colour- 
ing matter of shorl and the darker tourmalines, will shew, I think, that the older view 
regarding the condition of the iron in these minerals is really the correct one. 
Manganic oxide, it is well known, constitutes an intensely colouring matter as regards 
vitreous compounds. The finer black beads and ‘‘ bugles,” for example, are coloured 
entirely by about 10 or 12 per cent. of that oxide, the presence of a little boric acid appar- 
ently intensifying the reaction. But, as regards black tourmaline, manganese may be left 
out of consideration, because its amount, whether present as Mn’ O* or otherwise, is 
altogether insufficient to produce the black colour and opacity of the mineral. Many, if 
not most, varieties of schorl shew, under blowpipe treatment with sodium carbonate and 
nitre, a very faint manganese reaction; and the amount of manganese in green and red 
transparent or translucent tourmalines is higher, as a rule, than in black tourmalines. 
Hence the black colour cannot arise from the presence of manganese. Neither can it be 
due to any componnds of titanium, uranium, etc., the absence of these being fully proved 
by analysis. 
It is to the iron, therefore, that we must evidently look as the source of this black 
colour and opacity,—unless the color be regarded as due to the presence of carbon or 
carbonaceous matters, or to the problematical existence of a black allotropic condition of 
the silica or other component present in the mineral. 
Carbonaceous matter, we know, is frequently present in examples of quartz, obsidian, 
etc.; but this burns off more or less readily during ignition, while black tourmaline, 
even in fine powder, exposed to prolonged ignition in the muflle, retains its black colour, 
or assumes merely a brownish tint upon the surface. 
