60 MINERALOGY. 
with tellurium. These tellurids are known by their partial volatilization 
when heated in a glass tube, giving off vapor of tellurous acid, which is 
deposited on the sides of the tube. On applying additional heat to this 
deposit, it first melts and then evaporates. 
These combinations are very rare, and not very widely diffused. Those 
best known are graphic tellurium, white tellurium, laminated tellurium, and 
auro-tellurite, being mostly combinations with gold, silver, lead, copper, 
sulphur, &c. Those which principally occur in Transylvania are valuable 
mainly for the gold they contain. 
Class 4. Antimonids.—H aAusMANN. 
These also are known by their behavior when heated in a glass tube. 
The vapor, however, which is deposited in a crust on the sides of the tube, 
volatilizes on being heated without first melting like the tellurids. 
1. Antimonial Silver. 
This ranks among the rich ores, as it contains 77—84 parts of silver to 
23—26 of antimony in 100. Its specific gravity is 9.4—9.8; it is harder 
than calcareous spar, and is of a silvery tin-white color. When heated on 
charcoal it becomes converted into a brittle granule of antimonial silver, 
and, on continuing the heat, the antimony is all driven off in a white vapor, 
leaving the silver pure. It is somewhat brittle, a little ductile, and crystal- 
lizes in forms of the trimetric system (pl. 33, fig. 39), which are often 
grouped as in fig. 47. It is found in granular masses at Wolfach and 
Andreasberg. 
2. Antimonial Nickel. 
This consists of two equivalents of antimony and one of nickel. Its color 
is a light copper-red, running into violet; its fracture is uneven, small sub- 
conchoidal ; it is harder than fluor-spar; it crystallizes in double six-sided 
pyramids ( pl. 32, fig. 72), and in thin hexagonal plates. The principal 
locality is at Andreasberg in the Hartz. 
Class 5. Arsenids.—H aAusMANN. 
Combinations of arsenic with electro-positive metals. They are charac- 
terized, like the antimonids and tellurids, by giving out a white coating to 
the upper part of the glass tube within which they are heated, which is 
volatilized by additional heat, without melting. They give out, however, 
when heated on charcoal before the blowpipe, the peeuliar garlic-like odor 
of arsenic. 
1. Copper Nickel. 
This is one of the most important of these combinations. It contains 
34—40 per cent. of nickel, and may be used as an ore of this latter metal. 
It is of a bright copper-red color, to which it owes its name, and besides 
arsenic, also contains cobalt, iron, lead, antimony, and sulphur. It is found in 
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