66 OBSIDIAN. 
106. WOOD OPAL appears to be wood that, by some 
extraordinary operation of nature, has been converted 
into opal. Some specimens exhibit, very beautifully, 
the ligneous texture. This kind of opal is chiefly cut 
into plates for the tops and bottoms of snuft-boxes. It 
is found in alluvial land in some parts of Germany and 
Hungary. Several years ago the trunk of a tree, pe- 
netrated with opal, and so heavy that eight oxen were 
requisite to draw it, was found in Hungar}'. 
PITCHSTONE FAMILY. 
107, OBSIDIAN is a kind of glass, generally of blackish 
colour, formed in volcanoes, from which it issues in thick 
streams. 
This substance has been used for various purposes. 
It is possible to cut and polish it; but its brittle ness and 
frangibility are so great, that, without much care, it will 
fly into pieces during the working. The reflectors of 
telescopes are sometimes formed of it. In Mexico and 
Peru obsidian is cut into mirrors ; and the inhabitants 
of those countries used formerly to manufacture it into 
knives and other cutting instruments. Hernandez says 
that he saw more than a hundred of these knives made 
in an hour. Cortez, in a letter to the Emperor Charles 
the Fifth, relates that he saw razors that had been formed 
of obsidian. The natives of Easter and Ascension Islands 
use this substance for cutting instruments ; and also for 
pointing their lances and spears, and, in place of flint, 
for striking fire with. According to the account that 
has been given by Pliny, the ancients sometimes formed 
obsidian into mirrors, and ornamental articles of dif- 
ferent kinds. The Danish lapidaries, who obtain con- 
siderable quantities of it from Iceland, cut it into snuff- 
boxes, ring-stones, and ear-pendants. 
Obsidian is found near Mount Hecla, and in other 
parts of Iceland. Sir George Mackenzie, during his 
journey through that island, observed an immense mass 
of this substance, which appeared to him to have been 
