46 CONTRIBUTIONS TO MINERALOGY. [bull. 262. 
formed by the replacement of pyrite by means of descending solutions 
of cupric sulphate. The deposition of the mineral was accompanied 
by the formation of quartz, chalcedony, and kaolin. In the porphyry 
the chalcocite ore along the veins begins 100 to 200 feet below the 
surface and continues to a depth of 400 feet, or even more, when it is 
usually replaced by pyrite, chalcopyrite, and zinc blende. 
WILX.EMITE. 
This rare silicate of zinc (Zn 2 Si0 4 ) was found by Mr. Boutwell in the 
form of very small grayish crystals on a fragment of garnet rock in 
the Modoc open cut, on the north side of Modoc Mountain. These 
crystals were identified by Messrs. Pirsson and Penfield, of Yale Uni- 
versity, who state that the stout hexagonal prisms look exactty like 
those from the original localit}^ at Moresnet. 
CALAMINE. 
Small transparent orthorhombic crystals of calamine (ZnOH) 2 Si0 3 
were identified on a specimen of decomposed garnet rock from the 
Shannon mine, just above the lime quarry. 
DIOPTASE. 
The silicate of copper, dioptase (H 2 CuSi0 4 ) has been found at only 
a few localities. Veiy beautiful specimens, which, however, are by 
no means common, have long been known from the 
A~~ /\ classic locality, the Kirghese Steppes, Russia, and 
/ \ 6 / / \ \ more recently from the French Kongo State, Africa. 
\'./ \'*'^ ~\\ Dioptase is seldom found in the United States, the 
X/\ \ o\ \A only recorded occurrences being at the Bon Ton 
\ \. V._.-..\ Ai mines, Chase Creek, near Clifton, Ariz., noted by 
\ X'/y "\ / R- C. Hills/' and from near Riverside, Pinal County, 
\ /y \J Ariz., noted by W. B. Smith. 6 Well crystallized 
fig. 3.— Dioptase. specimens of this mineral were found on an old 
dump of the Stevens group of mines, on the w T esf- 
side of Chase Creek, near Garfield Gulch. They occurred in a small 
chimney of chrysocolla ore in limestone, now worked out, and the 
locality is believed to be the same as that described by Mr. Hills, j 
The dioptase crystals were submitted to Prof. S. L. Penfield, wh( 
remarks on them as follows: 
The crystals, measuring from 1 to 2 mm. in diameter, occur closely groupe< 
together, lining cavities in a brown ferruginous gangue impregnated with amorphou 
green material which is probably chrysocolla. The color of the dioptase is a beaut! 
ful emerald-green. The habit of the crystals, shown by the accompanying figure, i 
that which is most commonly observed and is especially characteristic for dioptase 
prism of the second order a (1120), terminated chiefly by the rhombohedron of th 
first order * (0221) and with small faces of the rhombohedron of the third order. 
a Am. Jour. Sci., ser. 3, vol. 23, 1882, p. 325. b Prdc. ' olorado Sci. Soc, vol. 2, 1887, p. IV.). 
