fiossik. 149 



The diamond ought certainly to be pla- 

 ced among the precious stones, but it is 

 different from all those above described. 

 Its combustibility is a property entirely 

 peculiar to itself; the diamond indeed 

 burns hi the same manner as phosphorus, 

 disappears without leaving any vestiges of 

 it behind. The diamond is supposed to 

 be pure carbon, and the radical of the 

 carbonic acid. 



There are several varieties of the dia- 

 mond, which differ from each other only 

 in colour ; some are^f a rose colour, and 

 others red, orange, yellow, green, blue and 

 dark coloured. 



Rock-crystal and quartz seem to be the 

 same stone* The name of rock-crystal 

 is given to that which is crystallized, and 

 of quartz to that which is in a rude mass. 

 The form of these crystals is a hexadral 

 prism, terminated at one of its extremities 

 and sometimes at both, by a summit com- 

 posed of six triangular faces. In hardness 

 they are inferior to all the other gems. 

 Rock-crystal consists almost entirely of 

 pure silex. Quartz enters into the com- 

 position of granite. 



Freestone is of the same i^ature as 

 N 



