116 



TRANSACTIONS OF THE 



leucite, the analcime and the garnet, which are com- 

 monly trapezohedral. The author will perhaps answer 

 that the trapezohedron belongs to the hexahedral sys- 

 tem : the same will be asserted for the octahedron, 

 tetrahedron and rhombal dodecahedron, which as pri- 

 mary forms are established as so many orders. For a stu- 

 dent, the primary forms are no easy task, which even 

 by the professors, are often differently expressed, and 

 frequently they are even doubtful : what Mr. Shepard 

 gives as a square prism is arranged by others as a square 

 octahedron ; and what he assigns as an oblique prism is 

 announced by some as an oblique octahedron, and other- 

 wise by others, which is not and cannot be the same to 

 the student. I will go further, in saying, that the sul- 

 phuret of manganese, from Transylvania and Cornwall, 

 is an hexahedron for Mohs, and that of Mexico is a 

 rhombohedron for me. Nay, Professor Mitscherlich 

 infers now from his observations, that every simple or 

 composed body is able to take two different forms of 

 crystals, which is the finishing blow even to the scien- 

 tific classification of minerals by crystallization. There- 

 fore, I propose to make as many orders as there are 

 crystals found in nature, and so the quadrangular and 

 hexagonal prisms, pointed and bevelled, should consti- 

 tute orders, like the regular hexagonal prism ; the stu- 

 dent, per se, will never find in his lifetime, however 

 long, that the quartz belongs to the order of the obtuse 

 rhombohedron. 



Returning again to the leucite, its edges and angles 

 are sometimes so worn that it is impossible to distinguish 



