452 Lindgren and Hillebrand — Minerals from Arizona. 



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 University, who state that the 

 stout hexagonal prisms look exactly like those from the original 

 locality at Moresnet. 



Calamine (ZnOH 2 Si0 3 ). — Small transparent orthorhombic 

 crystals of calamine were identified on a specimen of decomposed 

 garnet rock from the Shannon mine, just above the lime 

 quarry. 



Dioptase (H 2 CuSi0 4 ).— The silicate of copper, dioptase, has 

 been found at only a few localities. Yery beautiful speci- 

 mens, which, however, are by no means common, have long 

 been known from the classic locality, the Kirghese Steppes, 

 Russia, and more recently from the French Congo State, 

 Africa. Dioptase is seldom found in the United States, the 

 only recorded occurrences being at the Bon Ton mines, Chase 

 Creek, near Clifton, Arizona, noted by R. C. Hills,* and from 

 near Riverside P. O., Pinal County, Arizona, noted by W. B. 

 Smith. f Well crystallized specimens of this mineral were 

 found on an old dump of the Stevens group of mines, on the 

 west 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. The dioptase crystals were submitted to Prof. 

 S. L. Penfield, who remarks on them as follows : 



" The crystals, measuring from l mm to 2 mm in diameter, occur 

 closely grouped together, lining cavities in a brown ferrugi- 

 nous gangue impregnated with amorphous 

 green material which is probably chrysocolla. 

 The color of the dioptase is a beautiful emerald- 

 green. The habit of the crystals, shown by 

 the accompanying figure, is that which is 

 most commonly observed and is especially 

 characteristic for dioptase ; prism of the sec- 

 ond order a (1120), terminated chiefly _by the 

 rhombohedron of the first order s (0221) and 

 with small faces of the rhombohedron of the 

 third order x (1341). As is common on this 

 species, the prismatic faces are vicinal and 

 the s and x faces are striated parallel to their 

 mutual intersection edges, hence the crystals are not suited for 

 giving accurate measurements of the angles with the reflec- 

 tion goniometer. One crystal was measured, and the angles 

 of one of the rhombohedral zones, given below, are sufficiently 

 close to the calculated values to establish the identity of the 

 forms. 



* This Journal (3), vol. xxiii, p. 325, 1882. 

 fProc. Colorado Sci. Soc, vol. ii, p. 159, 1887. 



