MINERALOGICAL, ARRANGEMENT. 449 



are probably not as definite as they hav^ been some- 

 times considered. 



The proposed alphabetical arrangement will appear 

 to deviate the less from natural classification, if we 

 recollect that there is not any one strictly exclusive 

 natural order to supercede this arrangement, and re- 

 quiring that Zircon should be placed before or after 

 the siliceous genus; or that Lead should precede, or 

 follow, Iron or Copper. There may be conceived 

 to be as many natural classifications of minerals, as 

 there are natural properties common to the sub- 

 stances which are to be arranged. Thus, the metals 

 (not including the bases of the alkalies and earths) 

 might be arranged according to their fusibility, or 

 their specific gravity, or their ductility, &c. Either 

 of these characters might be adopted as the basis of 

 a natural classification , and the order of the substances 

 thus classed, would vary according to the generic 

 character we might adopt. 



The primary forms of most of the crystallised 

 minerals contained in the following alphabetical list, 

 are indicated in italics. The measurements there 

 given, are the most accurate I have been able to 

 obtain ; but although they have been taken with much 

 care, and probably do not vary much from the truth, 

 they are to be regarded in strictness only as approxi- 

 mations to the true angles at which the planes of the 

 crystals incline to each other. 



I have added where I could, to the square, rectan- 

 gular, and hexagonal prisms, the measurement of a 

 primary plane on some modifying plane, which fre- 

 quently occurs on the crystals ; and the class of 

 modifications to which the modifying plane belongs, 

 is indicated by its appropriate letter. 



3 L 



