ORES OF COPPER. 135 
the magnet; dissolves in nitric acid, with separation of 
sulphur. 
- Diff. '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 erwdbescite, from the Latin word for ¢o 
blush, alludes. 
Obs. Occurs, with other copper ores, in granitic and al- 
lied rocks, and also in stratified formations. ‘he 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 Ross 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 and barite. 
Massive varieties occur at the New Jersey mines, and in 
Pennsylvania. 
Crookesite. A copper selenide, containing 17°25 per cent. of thallium, 
and a little silver. : 
Domeykite, Algodonite and Whitneyite are copper arsenides ; Ber- 
zelianite, a copper selenide ; Hucairite, 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- 
black. Streak nearly like the color, 
sometimes inclined to brown and 
cherry-red. Rather brittle. H.=3- 
4°53. G.=4°5- 5-12. 
Composition. Cu, 8, Sb, (=4 Cu, 
S+8b, 8,), but with part of the cop- 
per replaced usually by iron and 
zinc, and sometimes silver or quick- 
silver, and part of the antimony b 
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 0 to 10 per cent. One variety from Spain in- 
cluded 10 per cent. of platinum, and another from Hohen- 

