ORES OF COPPER. 135 



the magnet ; dissolves in nitric acid, with separation of 

 sulphur. 



Biff. This ore is distinguished from the preceding by its 

 pale reddish-yellow color, and its rapidly tarnishing and 

 becoming of bluish and reddish shades of color, the quality 

 to which the name erubescite, from the Latin word for to 

 blush, alludes. 



Obs. Occurs, with other copper ores, in granitic and al- 

 lied rocks, and also in stratified formations. The mines of 

 Cornwall have afforded crystallized specimens, and it is there 

 called, from its color, " horse-flesh ore." Other foreign 

 localities of massive varieties are Eoss Island, Killarney, Ire- 

 land ; Norway, Hessia, Silesia, Siberia, and the Banat. 



Fine crystallizations were formerly obtained at the Bristol 

 copper mine, Conn., in granite; and also in red sandstone, 

 at Cheshire, in the same State, with malachite andbarite. 

 Massive varieties occur at the New Jersey mines, and in 

 Pennsylvania. 



Crooketite. A copper selenide, containing 17*25 per cent, of thallium, 

 and a little silver. 



Domeykite, Algodonite and Whitney ite are copper arsenides ; Ber- 

 zeliauite, a copper selenide ; Eucairite, a copper-and-silver selenide. 



Tennantite. A compound of copper, iron, sulphur, and arsenic. It 

 occurs in dodecahedral crystals, brilliant, with a dark lead-gray color, 

 and reddish-gray streak. From the Cornish mines near Redruth and 

 St. Day in Cornwall. 



Tetrahedrite. — Gray Copper. Fahlerz. 



Isometric and tetrahedral. Occurs in tetrahedral forms. 

 Cleavage octahedral in traces. 



Color between steel-gray and iron- -— -^^A 



black. Streak nearly like the color, /^-^^^-^ 

 sometimes inclined to brown and f^SPc"^""/" 7 / //'// 

 cherry-red. Rather brittle. H. =3- V\\\V //* 2 'y// 

 4-5. G. = 4 -5 5 -12. VV\ >g\ , </ 7/ / 



Composition. Cu 8 S 7 Sb 2 ( = 4 Cu 2 vo^^x^/w 

 S + Sb 2 S 3 ), but with part of the cop- ^J\\//^// 

 per replaced usually by iron and ^^zE^S'Hh/ 



zinc, and sometimes silver or quick- --^^J/ 



silver, and part of the antimony by 



arsenic, and rarely bismuth. It sometimes contains 30 per 

 cent, of silver in place of part of the copper, and is then 

 called argentiferous tetrahedrite. The amount of arsenic 

 varies from to 10 per cent. One variety from Spain in- 

 cluded 10 per cent, of platinum, and another from Hohem 



