67 
mostly truncated at the obtuse angles, like Fig. 19, or at the 
acute angles, as in Fig. 20, or united as twins and triplets. 
The colour varies from yellow and green to Frown and red, 
the streak is always lighter ; the lustre is half adamantine 
and half greasy, the fracture is conchoidal to uneven, the 
hardness 5*0—5*5, and the specific gravity 3-4—3-6. 
Pure crystals are almost always transparent, and may he 
cut and polished, so that they are used as precious stones 
for ornament. The constitution is titanate and silicate of 
lime. Ca Ti + 2 Ca Si. 
Sphene melts before the blow-pipe to a yellow-brown 
glass, and with salt of phosphorus gives a red pearl in the 
reducing flame. It is found especially at St. Gothard and 
in the Tyrol; the brown occurs in Saxony, Bohemia, and 
rarely in Scotland. 
Fig. 21.—Ilmenite, Titaniferous Iron. 
Crystallises like hematite in rhombohedrons, which are, 
however, generally truncated at the vertex and at the 
basal edges. It is iron-black, gives a brown-red streak, 
exhibits slight metallic lustre, is feebly attracted by the 
magnet, and consists of oxide of titanium, and the protoxide 
and the peroxide of iron. It occurs at Ilemengebirge, at 
Miask, and in small quantities at various localities in the 
United Kingdom. 
Fig. 23.—Tantalum Ores. 
Tantalum or Columbium is sparingly distributed in 
nature, and is only found in an oxidised condition, gene¬ 
rally as columbic acid in combination with niobic, pelopic, 
and tungstic acids, in various one-atom bases, such as the 
protoxide of iron and manganese, oxide of cerium, lime, 
magnesia, and yttria, frequently in very complicated rela¬ 
tions. Most of these combinations are iron-black, of sub- 
metallic lustre, very heavy and hard; the metallic acids 
mentioned appear to replace each other, so that sometimes 
one and sometimes another predominates. 
The Tantalite of Bodenmais, Fig. 23, also known as 
niobite and columbite, crystallises in right rhombic prisms, 
which are generally truncated at the lateral edges, as in 
Fig. 23, or they also exhibit truncations of the basal 
angles or edges. It is iron-black, of dark-brown streak, 
and feeble metallic lustre, opaque, of 6'39 specific gravity, 
and 6*0 hardness. It consists principally of the niobate 
and pelopate of the protoxide of iron; that from Tamela 
in Sweden is principally tantalate of the protoxides of iron 
and manganese; the tantalites of Finbo and Broddo con¬ 
tain in addition 8 to 16 per cent of oxide of tin. 
Fig. 22—24.— Wolfram, Tungsten. 
Wolfram or tungsten, likewise, only occurs in an oxi¬ 
dised state in nature, -and generally as an acid. The com¬ 
pounds are recognised by their high specific gravity, and 
until now have only been noticed in chemistry. 
Wolfram crystallizes in right rhombic prisms, which, 
however, are generally variously truncated at the basal 
and lateral edges, and also at the basal angles, as in Fig. 
22, of weak metallic lustre, iron-black colour and brownish- 
black streak. The fracture is uneven, the hardness = 5*0 
—5*5, the specific gravity 7*1—7*4. Twins occur fre¬ 
quently, sometimes also compact foliated masses, the 
crystals presenting very distinct horizontal striation. 
The elements are tungstate of the protoxide and per¬ 
oxide of iron. 
Before the blow-pipe it melts to a grey metallic glo¬ 
bule ; with borax it gives a greenish, in the inner flame 
with salt of phosphorus, it gives a red glass, and with soda 
in the point of the flame a blue enamel. It is soluble in 
hot nitric acid, by which the tungstic acid is separated as 
a yellow powder. It is found in the tin-ore mines of the 
primary formation, also at Neudorf in the Harz, in Styria, 
England, and France, and is used in the preparation of 
tungstic acids and its salts. 
Fig. 24.— Tungsten, Scheelite. 
Crystallises in square octahedrons, with corresponding- 
laminated structure, of greyish or yellowish white colour, 
vitreous to adamantine lustre, translucent, of 4*0—4*5 hard¬ 
ness and 6*0—6*1 specific gravity. It is tungstate of lime 
Ca W, and is soluble in hot nitric acid. It melts with 
difficulty to a translucent glass, gives a green pearl in the 
inner flame with salt of phosphorus, which on cooling be¬ 
comes blue. It is found in beautiful crystals at Zinnwald 
and Ehrenfriedersdorf in the Erzgebirge, in England, 
France, North America, etc., sometimes with tungstate of 
lead, frequently in very large crystals, rarely in compact 
foliated masses, which may be at once recognised by their 
remarkable specific gravity. 
PLATE XXII. 
Figs. 1 and 2.— Molybdenum Ores. 
Molybdenum was discovered by Scheele in 1778; it 
is silver-white, hard, ductile, difficult of fusion, of 8*6 spe¬ 
cific gravity, and does not occur native, but only in com¬ 
bination with sulphur or oxygen. 
Molybdenite, sulphuret of molybdenum, crystallises 
sometimes in hexagonal prisms, like Fig. 2. It is found, 
however, more frequently in foliated and scaly masses, as 
in Fig. 1, of bluish or lead-grey colour, and remarkable 
metallic lustre. It is opaque, flexible, readily gives off 
colour like graphite, and is unctuous to the touch, of 1*0— 
1*5 hardness and 4*5—4*6 specific gravity. The compo- 
rr 
sition is bi-sulphuret of molybdenum Mo. Before the 
blow-pipe it gives off sulphur, and burns gradually, leaving 
a deposit of molybdic acid. 
It is found in the tin mines of the Erzgebirge, Salzburg, 
Sweden, and Norway, in Cornwall, Cumberland, Argyle- 
shire, and other Scottish localities, and in North America. 
Molybdine is found as a sulphur-yellow earthy crust, 
sometimes with molybdenite, as in Fig. 1, and is generally 
a molybdic acid, rendered impure by oxide of iron, con- 
