65 
Fig. 27.— Silicate of Zinc. Smithsonite. 
The primary form is a right rhombic prism, which is, 
however, for the most part, truncated at the obtuse lateral 
edges and at the angles, as in Fig. 27. Very complicated 
crystals are found, which may be distinguished from the 
carbonate of zinc by their strong metallic lustre and trans¬ 
parency, twins also occur, as well as compact and botryoidal 
varieties. The colour varies from white and yellow into 
brown and blackish. The fracture is uneven, the hard¬ 
ness 5*0, the specific gravity 3*38—3TO. The con¬ 
stituents are silicate of zinc with 3 equivalents of w T ater, 
Zn 3 Si + 3 H. 
The Willemite is an anhydrous silicate of zinc, which 
crystallises in rhombohedrons and in hexagonal prisms, of 
5*5 hardness, and 3'93 specific gravity. It is found with 
the foregoing at Aachen, Raibl in Carinthia, and Franklin 
in New Jersey. 
Both minerals are employed for obtaining zinc along 
with the common calamine. Goslarite or zinc-vitriol is 
sulphate of zinc with 7 equivalents of water, and crystal¬ 
lises in right rhombic prisms of white and reddish colour ; 
soluble in water, of a metallic, astringent taste; it is found 
in crystalline stalactites and crusts in old mines, as a pro¬ 
duct of the decomposition of blende, as, for example, at 
the Rammelsberg near Goslar, and in Cornwall and Flint¬ 
shire. Sulphate of zinc is, however, generally produced 
artificially. 
PLATE XXL 
Fig. 1.—Cadmium. 
Cadmium is a bluish-white metal, first discovered in 
the year 1818, which is closely related to zinc, and has a 
specific gravity of 8*60—8‘69; it crystallises in regular 
octahedrons, is somewhat harder than tin, melts before the 
blow-pipe, takes fire in the air, and with sulphur gives a 
fine yellow pigment. It is found mostly in combination 
with zinc ores. 
Greenockite , Fig. 1, is pure sulphuret of cadmium, Cd, 
consisting of 77‘3 of cadmium and 22*51 of sulphur, and is 
as yet the only known compound of cadmium. It crystal¬ 
lises in hexagonal prisms, which are generally more or less 
bevelled at one end in combination with two pyramids, as 
seen in Fig. 1; there are, however, exceptionally also 
simple prisms. When heated in the retort, it decrepitates, 
and assumes a carmine red colour. When roasted on the 
charcoal it gives off vapours of sulphur without melting, 
and encrusts the charcoal with a reddish-brown oxide 
of cadmium. Until now it has only been found along 
with prehnite, in small holes, in porphyritic greenstone, at 
Bishoptown near Paisley, and a few other Scottish 
localities. 
Fig. 2—6.—Bismuth Ores. 
Bismuth occurs native, mineralised by sulphur, as an 
oxide, and in combination with silicic acid. Most of the 
ores are readily fusible, and before the blow-pipe give a 
yellow vapour, which is deposited on the charcoal, and 
with soda it yields a metallic grain. When dissolved in 
nitric acid, and mixed with water, it gives a white preci¬ 
pitate of basic nitrate of bismuth. 
Fig. 2—4.—Native Bismuth. 
Crystallises in cube-like rhombohedrons, as in Fig. 3, 
of a silver white colour, passing into yellowish and reddish, 
and of strong metallic lustre; it occurs also in crystal¬ 
line-foliated masses of rhombohedral foliated structure, as 
in Fig. 2, as, for example, at Redruth in Cornwall, or 
streaked like Fig. 4, disseminated, etc. The hardness — 
2*0—2*5, the specific gravity 9*73, the fracture foliated, 
and the friability so great that it is easily reduced to 
powder. It melts readily in the flame of a candle, and 
volatilises before the blow-pipe, while it leaves a yellow 
incrustation on the charcoal. Eight parts of bismuth melted 
with five of lead and three of tin, give the metallic mixture 
known as Newton’s fusible metal, which melts in hot 
water under 212°, and is therefore used for moulds of all 
descriptions. The solution in nitric acid is used as sym¬ 
pathetic ink; the paper is written over with it, and the 
writing disappears by drying, but is again restored by 
dipping in water, or by being brought into contact with a 
solution of sulphur. 
It occurs pretty frequently, especially in the primary 
rocks of Bohemia and Saxony, in France, England, 
Sweden, and Norway, and was formerly also found in the 
Schwarzwald. 
Fig. 5.—Bismuthine, Sulphuret of Bismuth. 
Crystallises in right rhombic prisms or needles, is 
found also disseminated and compact, crystalline-foliated, 
etc., of a lead-grey colour, sometimes with a variegated 
tarnish, brittle, of metallic lustre, opaque, of 2*0—2*5 
hardness, and 6*549 specific gravity. The composition is 
simple sulphuret of bismuth, occasionally rendered impure 
by a little sulphuret of copper; the latter is found at 
Schneeberg and Johann-Georgenstadt in Saxony, in Corn¬ 
wall and Cumberland, the pure bismuthine in Sweden, 
Hungary, etc. 
Fig. 6.-—Eulytine, Bismuth-blende. 
Crystallises in brownish-yellow pyramidal tetrahedrons 
of adamantine lustre, like Fig. 6, and twins of the same 
kind, of 4*0—5*0 hardness, and 5*9—6*0 specific gravity. 
The composition is essentially silicate of bismuth. It 
melts before the blow-pipe readily to a brown pearl, and 
leaves an incrustation of bismuth on the charcoal. 
It is found mostly along with bismuth ochre, or earthy 
oxide of bismuth, of yellowish colour, at Schneeberg in 
Saxony. 
Figs. 7—12.—Uranium Ores. 
Uranium occurs in nature only in an oxidised condi- 
