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viz. : heated before the blowpipe they were infusible and 
turned brown, not black, probably owing to one of two 
causes, either (1) the flame was not a pure oxidising flame, 
and a little of the cupric oxide was reduced to cuprous 
oxide ; or, (2) there was a slight admixture of quartz with 
the dioptase crystals. The presence of copper was proved 
by dissolving a crystal in a drop of hydrochloric acid, 
evaporating off the latter, redissolving the residue in a drop 
of acetic acid and adding potassium ferrocyanide, when 
the characteristic copper reaction was very marked. There 
was not the slightest effervescence on dissolving the mineral 
in hydrochloric acid, but flocculent particles of silica sepa- 
rated out. Mr. Hutchings obtained identical results in a 
chemical examination of the crystals. From the above tests, 
the crystallographical examination and the fine emerald- 
green colour of the crystals, there can scarcely be a doubt 
that they are really those of dioptase. Colourless quartz 
crystals were also observed associated here and there with 
the dioptase, but -f R and — R were both present, generally 
nearly in equilibrium, and the prism faces exhibited strongly 
the characteristic horizontal striation, therefore coupling the 
marked differences in colour and crystal-form a confusion of 
the two minerals could scarcely be possible. 
I believe this is the first instance observed of dioptase 
occurring simultaneously with chrysocolla, and according to 
my knowledge the first time it has been found in Peru, in 
fact out of Russia. The exact locality of the mine cannot 
unfortunately be ascertained. I am of opinion that the 
dioptase has been formed by the action of water upon the 
chrysocolla, the latter being a product of the decomposition 
of cuprite (which is always intimately associated with it) 
by a solution of silicic acid in water. Very fine botryoidal 
malachite sometimes occurs associated with chrysocolla and 
cuprite in the same locality in Peru. I hope shortly to 
obtain accurate measurements of the dioptase crsytals. 
