SERPENTINE* 
may be scratched with a knife, and the colour of 
the streak is a light green. It easily melts into a 
black glass, and is often found crystaUized in an ir- 
regular manner. Hornblende forms a constituent 
part of many rocks, end even forms entire mount- 
ains or slaty beds in mountains. It enters largely 
into the rocks of volcanic origin, such as green- 
stone, basalt, &c., generally denominated traj) rocks. 
The chemical composition of hornblende, basalt, 
and lava, is very similar. 
Hornblende often occurs in a crys- 
tallized form, as in the margin, though 
it is more often met with in rude, 
shapeless masses. We often see it 
composed of long, needle-shaped or 
acicular crystals, diverging from a cen- 
tre, which are star-shaped or radiated 
like the spokes of a wheel, and the 
histre is shining, 
Serpentine. — This is one of the magnesian min- 
erals, being composed of from 20 to 45 per cent, of 
siiex, 18 to 23 per cent, of alumine, and 23 to 34 of 
magnesia, and 8 to 12 of water, with a trace of iron, 
to which its colours are often owing. It derives its 
name from its resemblance to a serpent's skin, being 
streaked or spotted. Bakewell thinks that it may 
be regarded as an intimate combination of horn- 
blende with talc or chlorite; whether this be the 
case or not, it is certain that there is an intimate 
connexion between them, and that W6 often find 
hornblende changed into serpentine when in con- 
tact with limestone. Serpentine is generally com- 
pact, nearly granular, yields to the knife, is some- 
what soapy to the feel, and is susceptible of a high 
polish. It is often employed as a marble ; and, when 
limestones containing it are polished, they consitute 
what is called the verd antique marble. This mineral 
