. 250. CHARACTERISTIC. 387 



not from the genus Tin-ore. The form of the pyramidal 

 system, and the uncoloured streak, shew that it belongs to 

 this genus. If we compare the individual with the remain- 

 ing generic characters, we find that it is excluded from the 

 genus Scheelium-ore by its too great hardness, and too 

 little specific gravity ; from the genera Tantalum-ore, Ura- 

 nium-ore, Cerium-ore, Chrome-ore, Iron-ore, and Man- 

 ganese-ore, by hardness and specific gravity, both of 

 them being too great; as also by its uncoloured streak, 

 which only agrees with that genus from which the indivi- 

 dual differs most by its hardness and specific gravity. From 

 all this we infer that the individual cannot belong to any 

 other than to the fourth genus, and that we are therefore 

 entitled to give it the name of Tin-ore. 



This genus contains but one species. The conclusion that 

 the individual must belong to this species, might never- 

 theless be erroneous. There could exist a second species of 

 this genus. Hence we must accurately consider the di- 

 mensions of the forms. If these coincide with the angles 

 given in the character, the highest degree of certainty, that 

 the individual belongs to or is pyramidal Tin-ore, will be 

 obtained. 



The perfect determination of an individual depends, as the 

 above example has shewn, upon the possibility of correct- 

 ly ascertaining those three properties : viz. form, includ- 

 ing cleavage ; hardness ; and specific gravity. If one or 

 the other of these characteristic marks be wanting, the de- 

 termination will remain incomplete. It does not, however, 

 become prejudicial to the method, that minerals of this 

 kind cannot thoroughly be determined by its assistance. 

 It is exactly the same in the other parts of Natural His- 

 tory, in Zoology and Botany. The characteristic proper- 

 ties must be completely observable, otherwise a complete 

 determination will be impossible. In Mineralogy the 

 Characteristic affords sometimes more : it leads to a cor- 

 rect determination, even if the knowledge of the forms re- 

 mains imperfect, or if it is entirely wanting. But such a 

 determination wants evidence (. 246.) j and for this reason 



