ON THE PRIMITIVE FORM OF CRYSTALS. 341 



The new and beautiful system of crystallography, 

 proposed by Professor Mohs of Freyberg, and of 

 which a general account has been published in the 

 5th number oi the Edinburgh Philosophical Jour- 

 nal, harmonises in a very singular manner with the 

 optical arrangement of minerals*. 



M. Mohs divides crystals into four great Series, 

 viz. 



1. The Rhomboidal system. 

 % The Pyramidal system. 



3. The Prismatic system. 



4. The Tessular system. 



None of these forms are capable of being derived 

 from one another, and therefore each of them, as 

 well as their combinations, must remain entirely 

 distinct from the rest. 



The following Table will point out the relation 

 between the Primitive Forms of Hauy, the Funda- 

 mental Forms of Mohs, and the classes derived 

 from the number of axes of Double Refraction. 



• It is peculiarly remarkable, that M. Mohs' system ren- 

 ders it necessary, that the right quadrangular prism with a 

 square base should be transferred to the First Class of Primi- 

 tive Forms, and placed beside the octohedron with a square 

 base. 



Tabular 



