Prof. J. F. Blake—Glaucophane in Anglesey. 125 
X.—On THE OcCURRENCE OF A GLAUCOPHANE-BEARING Rock 
In ANGLESEY. 
By Prof. J. F. Buaxe, M.A., F.G.S. 
HE occurrence of glaucophane has not, I believe, been previously 
noted in Great Britain, and as it is a mineral of some interest, 
my friend Mr. Teall has suggested that a separate notice of it should 
be given. It would otherwise be naturally described in the Report 
on the Microscopic Structure of Anglesey Rocks to be presented to 
the British Association at their forthcoming meeting. 
The rock which contains the mineral in question has already, in 
a certain sense, been described by Prof. Bonney in the Quarterly 
Journal of the Geological Society, vol. xxxv. p. 3808, in the follow- 
ing words :— 
“XII. Quarry NEAR ANGLESEY Monument. 
“A foliated dense felted mass of a dull greenish, rather decidedly 
dichroic mineral (probably a species of chlorite), and of small 
greenish yellow epidote crystals, with a few angular fragments of 
quartz (?), and two or three scales of mica (? paragonite).” 
This description shows that the specimen which afforded it was 
one in which the glaucophane had gone over into chlorite, which it 
very frequently is found to do. In fact, there are many exposures 
of rock around the Anglesey Monument and to the south of it, 
which obviously, from their mode of occurrence and their connection 
with each other, all belong to the same mass, and their minute 
structure is of the same type; but in most the colouring mineral is 
a chlorite, and only in some of the freshest exposures, or in particular 
spots, is the original glaucophane seen. Elsewhere, by identity of 
structure and mode of recurrence, we may still recognize portions 
of the same mass in which the mineral is ordinary hornblende. 
These rocks have been hitherto taken to be identical with the 
dark schists of the district in which the prevailing mineral is 
chlorite, and only recently has Dr. Callaway, at the British Associa- 
tion, come round to consider some of them igneous. 
The beautiful blue tint of the glaucophane gives a very rich aspect 
to the rock under the microscope, by which the long crystals of this 
mineral are seen enwrapping and felting over the short crystals of 
epidote. The rock is so very foliated, in such excessively fine lines, 
and these are so beautifully contorted, that I had much difficulty 
at first in recognizing it as igneous; and since, according to my 
experience, hornblende in Anglesey is limited to igneous rocks, 
I had great difficulty in believing this blue mineral could really be 
glaucophane, which is only a variety of hornblende. However, I 
showed it to M. Renard at the meeting of the British Association, 
and he thought it would probably be glaucophane, and I therefore 
had a transverse section cut, and that set the matter at rest. 
Prof. Rosenbusch in his “ Mikroskopische Physiographie,” p. 471, 
gives the following as the characters of Glaucophane :— 
