Analysis of Idocrase. 85 
Very fine crystals of unusual size occur in the gravel along 
the bank of the stream. icked up several that were two 
inches long and three quarters of an inch in diameter. ‘They have 
a delicate pink or rose color and some of them are translucent. 
The peculiar tesselated appearance displayed in a cross section o 
crystals of this species, is exhibited by these specimens in a beau- 
tiful manner, 
Caxcrre.—Crystallizations of this mineral are found at the 
Quicksilver mine, (New Almaden), at the Pass of Jacum, San 
Diego Co, and on the surface of the Colorado desert north of — 
Carrizo creek, where some transparent crystals were picked we Pv 
It also occurs in beautiful stalactites and me crystals in the 
great cave in Calaveras Co. » 
Art. IX.—Analysis of Fdocrase from Duckioon, Polk Co., 
Tenn. ; by J. W. Maurer, Ph.D. 
Tue specimen of this Idocrase examined ccna among some 
other minerals from the Ducktown copper mine, in thin bladed 
crystals imbedded in a mixture of copper and iron pyrites. The 
crystals were from half an i h to two inches in length, about 
, 1,0, l-w, and o-o, the last being most developed, and the - 
others very small. The mineral was nearly colorless, exhibiting 
transparent. H. =6°5; sp. 
Analysis gave the following results, a little copper present be- 
ing calculated as copper pyrites (derived from the gangue), and 
the necessary amount of iron subtracted from the total quantity 
of oxyd of iron weighed: Atoms. 
ilica, - - - 38°32 . $46 
Alumina, + - - 2568 ae =< 
Protoxyd of iron, - 8-13 22 | 
Lime, : ~ ° < - Qe39 907 gro 
Magnesia, - - - 36 018 
Copper pyrites, - ~ ae 
9979 
We have here a slight excess of alumina over the amount re- 
quired by the formula 3RO, SiOs+Al20s, SiOs, and a slight 
defect of protoxyds. The fragments of mineral were selected 
with great care, and contained no visible particles of gangue— 
hence the copper found in the analysis may perhaps, as in Cyprine, 
belong to the Idocrase itself, in which case the protoxyds would be 
__ increased by tbe copper and iron calculated above as copper pyrites. 
"Fs 
z a 
