155 
Ordinary Meeting, April 16th, 1878. 
E. W. Binney, F.R.S., F.G.S., President, in the Chair. 
“ Note on the Occurrence of Dioptase on Chrysocolla, from 
Peru/' by Charles A. Burghardt, Pb.D., the Owens 
College. 
A short time ago, Mr. W. M. Hutchings, F.C.S., of 
Birkenhead, sent me some specimens of chrysocolla 
(CuSi0 2 -f-2H 2 0), from Peru, accompanied with a statement 
that there were some minute crystals in a cavity in one or 
two of the specimens which might possibly prove to be the 
rare mineral dioptase (CuSi0 2 +H 2 0). I proceeded to make 
a crystallographical and chemical examination of the crys- 
tals, and found that although extremely small, the forms 
could be recognised under the microscope. The chrysocolla 
mass is eaten into in one or two spots, cavities being pro- 
duced which are divided into numerous cells by the inter- 
section of thin partitions of chrysocalla substance. The 
dioptase crystals occur particularly fine in small green tufts 
and sheaves attached to the partition walls of the cells, whilst 
those crystals clothing the interior of the cells are not so 
well developed as the others. The measurements so far 
obtained have not been satisfactory, owing to the extreme 
smallness of the crystals, but the forms observed are those 
peculiarly characteristic of dioptase, viz. : c©P2 — 2R ; the 
rhombohedron being extremely well defined. No other 
forms were observed, but a great many fine acicular sub- 
individuals growing parallel with each other build up a 
large individual. Some of the crystals I carefully picked 
out and examined chemically with the following results, 
Proceedings — Lit. & Phil. Soc. — Yol. XYII. — No. 12. — Session 1877-8. 
