oO 
SILICA. yea ( 
The effect is owing to filaments of asbestus. It comes from 
Ceylon and Malabar, ready cut and polished, and is a gem 
of considerable value. 
Flint, Hornstone. Massive compact silica, of dark shades 
of smoky gray, brown, or even black, and feebly translucent, 
it breaking with sharp cutting edges and a conchoidal sur- 
face. Flint occurs in nodules of chalk: not unfrequently the 
nodules are in part chalecedonic. Hornstone differs from 
flint in being more brittle ; it is often found in limestone. 
Chert is an impure hornstone. Limestones containing 
hornstone or chert are often called cherty limestone. 
Plasma. <A faintly translucent variety of chalcedony ap- 
proaching jasper, of a green color, sprinkled with yellow 
and- whitish dots. 
III. JASPERY VARIETIES. 
Jasper. A dull red or yellow siliceous rock, containing 
some clay and yellow or red iron oxide, the red, the anhy-: 
drous oxide, and the yellow, the hydrous oxide. Heat drive 
off the water from the yellow jasper and turns it red. It 
also occurs of green and other shades. iband jasper is a 
jasper consisting of broad stripes of green, yellow, gray, 
red, or brown. Lgyptian jasper consists of these colors in 
irregular concentric zones, and oceurs in nodules, which 
are often cut across and polished. adn jasper is a variety 
with delineations like ruins, of some brownish or yellowish 
shade on a darker ground. Porcelain jasper is nothing but 
a baked clay, and differs from jasper in being fusible before 
the blowpipe. Red felsyte resembles red jasper; but this 
is also fusible, and consists largely of feldspar. 
_dasper admits of a high polish, and is a handsome stone 
for inlaid work, but is not much used as a gem. 
Bloodstone or Heliotrope. Deep green, slightly trans- 
lucent, containing spots of red, which have some resem- 
blance to drops of blood. It contains a few per cent. of 
clay and iron oxide mechanically combined with the silica. 
The red spots are colored with iron. There is a bust of 
Christ in the royal collection at Paris, cut in this stone, in 
which the red spots are so managed as to represent drops 
of blood. 
Lydian Stone, Touchstone, Basanite. Velvet-black and 
opaque, and used, on account of its hardness and black 
color, for trying the purity of the precious metals; this is 
