12 



TAB. CCCVIII. 



Cubic Calcedoni/. 



1 his is commonly called Cubic Hornstone, but is truly 

 a Calcedony, as indeed are many things which are com- 

 monly called Hornstone, and it is hard to show their di- 

 stinguishing characters. This specimen came from Beer 

 Alstone, where the curious Octaedral Fluor is found on 

 what is also called Hornstone — see tab. 26. The crystals are 

 generally blunt edged, their solid angles truncated, and their 

 surfaces minutely mamillated, which helps to distinguish 

 them. This secondary crystallization almost exclusively 

 belongs to this substance, although there are one or two 

 instances of its being found in other substances, as in 

 Steatite, but which is chiefly in the form of Quartz. All 

 are scarce. 



The name Hornstone I suppose to be taken from the re- 

 semblance the stone bears to horn ; a great variety of stones 

 have occasionally had that appellation given to them, which 

 probably vary much in their ingredients, as some little 

 mixture may help their appearance : thus we might possibly 

 find Lime, Fluor^ and Clay Hornstones. 



