. 249. CHARACTERISTIC. 383 



. 84$. USE OF THE CHARACTERISTIC. 



The use of the Characteristic is the same in Mi- 

 neralogy as in Zoology and Botany. 



It will be useful to give a short explanation of the pro- 

 cess used in the determination of minerals. 



If a mineral is to be determined, first its Form, if this 

 be regular, must be ascertained, at least as far as to know 

 the system to which it belongs. Then Hardness arid Speci- 

 fic Gravity must be tried with proper accuracy, and express- 

 ed in numbers. It is sufficient, however, to know the lat- 

 ter to one or two decimals. The specific character requires 

 these data ; they are also of use in the characters of the 

 classes, orders, and genera. After this examination, the 

 Characteristic may be applied, and it will at the same time 

 point out what other characters are still wanting ; so that 

 a mere inspection of the mineral, or a very easy experi- 

 ment, as, for instance, to try the streak upon a file, or still 

 better, upon a plate of porcelain biscuit, will very often be 

 sufficient. The given individual is now carried through 

 the subordinate characters of the classes, orders, genera, 

 and species, one after the other, comparing its properties 

 with the characteristic marks contained in the characters of 

 these systematic unities. From their agreement with 

 some, and their difference from other characters, we in- 

 fer, that the individual belongs to one of the classes, to 

 one of the orders, to one of the genera, and to one of the 

 species. Having advanced in this manner to the character 

 of the species, it will in some instances be necessary, and 

 in all cases advisable, for the sake of certainty (. 246.), to 

 have recourse to the dimensions of the forms. This is 

 particularly necessary, if the genus, to which the mineral 

 belongs, contain several species having forms of the same 

 system, as is the case in the genus Augite-spar. The com- 

 mon goniometer in most cases will suffice for determining 

 the dimensions of the forms, the differences in the angles 



