• 704 
Tourmaline is in short stunted prisms, very pleochroic, varying from red, pink, 
yellow, and green to blue. Often the tourmaline is in rounded grains. 
Biotito in hexagonal brown plates, very small. No magnetite, and very little 
apatite. 
CooKTOwiT (Queen sijAitd). 
A. J. Madden, Esq., Collector. 
Tourmaline and cassiterite associated with quartz. 
Although this aggrcgale of minerals has no place amongst the granites, it comes 
in with some advantage here, because Plate 63, fig. 2, illustrates a tourmaline crystal in 
quartz from the same Cooktovvii district. The tourmalines drawn on the plate show the 
pleochroism and the cleavage of the microscopic tourmalines in the Cook district. The 
section was prepared from a piece of quartz-carrying cassiterite and tourmaline, forming 
part of a large sample of tin ore sent for assay by A. J. Madden, Esq., of Cooktown. 
The exact locality is not known to me. The ore is typical of over a hundred samples 
assayed by myself from time to time from the neighbourhood. The tourmalines tend 
to separate into segments transverse to the principal axis (Le., along the cleavage), quartz 
filling up the spaces left. The quartz so introduced between the segments “ orients ” 
uniformly with that contiguous to the sides of tourmalines. The quartz does not 
always uniformly polarize, however ; much of it is in the form of granulitic aggregates. 
These aggregates often, but not always, border large grains of quartz, separating it from 
its neighbours. In these quartzes the tourmalines pass through larger grains and 
aggregates, sometimes being separated into segments in the larger crystals, and at 
others in the suture. 
The interesting question arises, which of the two minerals is the first born. 
Eosenbusch says* that “ tourmaline is not directly secreted out of the eruptive magma 
in eruptive rocks, but resulted from the action of fumaroles, carrying fluorine and 
boron, on the erujjtive rock, especially on its felspar and mica.” Teall also alludes to 
the action of fumaroles in the genesis of tourmaline. This would rather support the 
pre-existence of the quartz. On the other hand, the uniform orientation of the quartz 
between and alongside of the broken prisms would lead one to think that the 
reverse was the case. Could it be that the tourmaline crystallised out in the 
quartz by the action of fumaroles, as above, while the quartz was viscous and under 
pressure, and that earth-stresses and dynamic motamorphism followed, separating the 
prisms, after which the quartz proceeded to crystallise ?t 
Cassiterite is in brown, gum-like drops, sometimes honey-yellow, included between 
tourmaline prisms. 
Quartz very dusty and, under the ^-inch objective, shows yellow, yellowish-red, 
and red flecks, probably hydrated oxides of iron. The inclusions are very numerous, 
but exceedingly minute. Some are liquid ; others might be liquid with gaseous 
envelopes, but this has not been definitely ascertained. Certainly some of the inclusions 
contain oscillating bubbles only visible under the ^-inch. In all of the section prepared of 
this rock or sample of tin-bearing quartz, the tourmalines were sharp and highly 
* “Microscopical Physiography,” p. 184. 
t Since these slices were prepared Mr. Jack has shown me a most striking example of the parting of 
tounnaline in quartz, the u^iartz having filled np the spaces between the segments just as in the above 
samples, but the evidenoe of dyti,amic met.amorphism is much more striking in this a.ample (which comes 
from the .same district, and, I strongly suspect, from tlie same mine). Mr. Jack’s specimen shows how the 
tourmaline has also been bent out of tlie straight, small bundles of the prisms following the curve. The 
bundle of tourmaline crystals forms a flagellum about four inches in length. The specimen came from the 
Mount Leswell Tin Mine, Cooktown. 
