COMMON CLAY. 71 
Aclularia is said to have been first discovered by an 
Italian mineralogist, near Mount St. Gothard, in Swit- 
zerland. He named it Adularia felspar, in the belief 
that the mountain on which he had found it was named 
Adula. This, however, was not the case ; for Mount 
Adula is at some distance from St. Gothard, in the 
Grisons. This mineral has since been found in the 
granite of the island of Arran, in France, and Germany. 
The finest specimens are brought from Ceylon. 
//. SOFT STONES : those which will not scratch Glass. 
114. CLAY FAMILY. 
Clay is a mixture of alumine (33) and siiex (38), and is too 
well known to require much description. 
It is opaque, has an earthy texture, is about twice as heavy 
as water, when moistened is very ductile, adheres slightly to 
the tongue ; and with its peculiar smell (called clayey) every 
one is acquainted. 
115. COMMON CLAY, or POTTER'S CLAY, which 
is found in nearly every country of the world y is sometimes 
whit e 9 has a blue or yellowish tinge, or is brown or reddish. 
It is the peculiar quality of this substance to become 
so hard by heat that it will even strike fire with steel. 
The ductility of clay, and its property of thus harden- 
ing in the fire, have rendered it an article of indispen- 
sable utility to mankind in all civilized countries. It is 
formed into eating vessels of almost every description ; 
plates, dishes, cups, basins, bowls, and pans for keeping 
provisions in. For these almost any kind of clay may 
be advantageously used ; but it is necessary to mix it 
with sand, for the purpose of rendering the vessels 
