20 
II. HORNBLENDE AND AUGITIC MINERALS. 
These are combinations of magnesia and of oxide of 
iron, with silicic acid, which resemble the foregoing mine¬ 
rals in hardness, are mostly dark green or blackish, and 
present a splintery fracture. They belong either to the 
primary or to the volcanic rocks, often colouring the latter 
grey or black. 
Figs. 14 and 15.— Augite, Pyroxene, Diopside, Baika- 
lite, Malacolite, Sahlite, Coccolite, Volcanite, 
Basaltine, Pyrgome, Fassaite. 
Augite belongs to the series of hornblende minerals, 
from which it is less distinguished by its elements than by 
the difference of its crystalline angles, and its occurrence, 
in so far as it is principally found in volcanic forma¬ 
tions. The primary form is an oblique rhombic prism 
of 87° 5', and 92° 35'; the terminal planes are inclined 
to the sides at an angle of 100° 10'. The crystals 
may be split in the direction of the lateral and terminal 
planes, and of the truncated planes of the obtuse lateral 
edges. 
The colour varies from black, through brown and green, 
to grey and white, hence the different names. The black 
and brown varieties are called common augite , the dark 
green baihalite, the light green and white diopside , the 
grey chalky varieties malacolite and sahlite, the small gra¬ 
nular greenish and brown pyrgome and fassaite, and the 
compact foliated and granular varieties are called coccolite. 
TJralite is the name given to an augite from the Urals, 
which has the chemical composition of hornblende, and the 
crystalline form of augite. 
The constituents are silicate of magnesia with silicate 
of lime, and the protoxide of manganese and iron. 
'The hardness is equal to 5*0—6*0 ; the specific gravity 
= 3T5—3*50. Before the blowpipe, it melts tolerably easily 
to a green or black glass. It is insoluble in acids. Very 
fine transparent crystals are found in Piedmont (Fig. 15), 
at the Lake Baikal in Siberia, and in the Zillerthal; the 
black varieties, the truncation of whose obtuse lateral 
edges and acute basal angles is represented in Fig. 14, 
occur principally in the volcanic rocks, as, for instance, in 
the Fassathal, at Vesuvius, in the neighbourhood of Rome, 
at the Kaiserstuhl, etc. Thev form an essential element 
* *j 
of the basalts and dolomites, of most lavas, and of the 
augitic porphyry. 
The transparent crystals from the Zillerthal are some¬ 
times cut as stones for rings, and sold at about a couple 
of shillings each. 
Figs. 16-18.— Hornblende, Amphibole, Pargasite, Iva- 
rinthine, Actinoltte or Strahlstein, Tremolite or 
Grammatite, Asbestus. 
Crystallises in oblique rhombic prisms of 124° 34', and' 
55° 26'; the prisms, therefore, appear more decidedly rhorn- 
boidal than those of the augites, as a glance at Fig. 16, one 
of the usual forms of the so-called actinolites, will show. 
Truncation of the acute lateral edges and of the acute angles 
also occurs as in Fig. 17, which represents the so-called 
basaltic hornblende from Bohemia. It occurs, moreover, in 
crystalline fibrous, granular and compact masses. The long 
and finely fibrous varieties, like Fig. 18, are called asbestus ; 
if the fibres are white, long, and delicate, amianthus, earth- 
flax, and mountain-silk; the varieties with confused and 
curved fibres, and which are light and porous, receive the 
name of mountain-cork and mountain-leather. The short 
and thick fibrous, white, grey and reddish varieties, if they 
feel sharp, and have a silky lustre, are called tremolite. 
The hardness is = 5*0—6*0, the specific gravity = 
2*9—3*2. The constituents are, silicate of magnesia, silicate 
of lime, and the protoxides of iron and manganese, but in 
proportions different from those of augite; sometimes a 
part of the silica is replaced by alumina. 
Before the blowpipe, hornblende melts to a whitish or 
dark green glass; with salt of phosphorus, the splinters 
leave a skeleton of silica. 
Hornblende forms an essential element of syenite, 
diorite, aphanite, greenstone, hornblende schist, horn¬ 
blende rocks, and especially of the plutonic rocks; it is 
also found, however, in the matter thrown out by eruptions 
of Mount Vesuvius, and in many lavas, as, for example, 
in the so-called breislaldte, a cupriferous acicular asbestus 
from Vesuvius and Etna. 
As hornblende, especially if it is mixed with the rocks 
in thin layers and acicular forms, presents a marked curve, 
and is difficult of separation, it gives to these rocks a cer¬ 
tain solidity, so that they are preferred to most kinds of 
stone for the construction of roads and pavements, some¬ 
times also for monumental purposes; to this class belong 
the diorites and hornblende stones ; the green porphyry 
(Plate VI. Fig. 6), which was formerly used try' the ancients 
for the decoration of temples and palaces, owes its colour 
also to hornblende, as well as the black porphyry (Plate 
VI. Fig. 7). 
Asbestus is applied to the manufacture of incombus¬ 
tible gloves and cloths; the varieties known under the 
names of mountain-silk or earth-flax, are found principally 
in the serpentine and micaceous schists of Switzerland and 
the Tyrolese Alps. 
Fig. 19.— Hypersthene, Paulite. 
The primary form is a right-rhombic prism of 98° 12'; 
it is found generally, however, only in crystalline foliated 
masses, from which fragments like Fig. 19 may be broken. 
The colour, between a greyish-black and copper-red, 
inclines also to brown and green. The hardness = 6 - 0, 
the specific gravity =3*39—3*60. The constituents are 
the same as in augite, only that the protoxide of iron 
occurs in greater quantity. Very difficult of fusion, which 
can only be effected when it is reduced to the smallest 
possible splinters. This mineral is distinguished from 
hornblende by a certain metallic lustre, and, when cut, 
receives a good polish, so that it is sometimes used as a 
stone for ornament. 
