536 
Proceedings of the Royal Irish Academy. 
takes place in other minerals. It is curious that while in most mine- 
ralogical treatises the interchangeability of the protoxides of iron, man- 
ganese, calcium, and magnesium is pointed out, that of zinc with these 
— so far as I am aware — has not been yet shown ; and in the very few 
instances in which it is given as an accessory metal, its presence ap- 
pears to be considered rather as an accidental circumstance than as the 
result of any chemical law. In no case has it been given in the com- 
position of a mineral, unless present in such quantity as to make a very 
serious item in the analyses, as in those of Automolite, or zinc 
spinel (20 to 35 per cent. ZnO) and Franklinite (17 per cent. Zn 0).'''' 
Yet with regard to most minerals, traces of manganese, iron, mag- 
nesium, &c., are constantly recorded as replacing part of the essential 
metals. 
Believing, therefore, that zinc compounds might thus be expected 
to exist in most magnesian rocks or minerals, I have examined several, 
and, so far, the result has almost exceeded my anticipations, for in 
every case the metal has been proved. As yet I have merely satisfied 
myself as to its presence, reserving quantitative determination until I 
shall have completed the qualitative examination of a number of speci- 
mens ; but it may be well to mention the rocks and minerals already 
tried. 
1 . CTialh, from Legmurn and Slieve Gallion ; already described. 
2. Basalt l^o.l. 
3. Granite,] Wicklow and Wexford Uange variety, from Graigue- 
na-Spiddoge, near Carlow : obtained from the heart of the quarry. 
{a) A very coarse-grained, light-coloured rock, porphyritic in parts, 
containing white mica and a dark greenish magnesian variety ; also 
tourmaline. The portion submitted to analysis was prepared in such 
a way as to have as much mica as possible present. Eour analyses of 
this were made in the wet way, as well as others with the blowpipe, 
ere I allowed myself to be perfectly satisfied as to the presence of zinc. 
The quantity was very small, as was, of course, to be expected. Traces 
of copper and lead were also observed. 
(J)) Mica. — After many searches at the same quarry, I was able to 
obtain a mass of mica sufficiently large for analysis with the blow- 
pipe ; J it was mostly white mica, but contained numerous laminae of 
green mica. 
About four grains at a time were treated with carbonate of soda, on 
charcoal, before the blowpipe. Two metals were reduced, which proved 
to be copper and zinc. The zinc spangles dissolved with rapid evola- 
* Is it not possible that Franklinite is a Magnetite with the ferrous iron replaced by- 
zinc? Spinel is a magnesian mineral, and its accessory metals belong to the same iso- 
morphous group. 
t Automolite has been found in granite, at Haddam. Dana's Manual of Mineralogy, 
p. 161. 
X In all cases the blowpipe gave very distinct results, even where a large quantity 
of material ^vas required for decided reaction in the wet analyses. 
