CHARACTERISTIC. 151 



exclusive terms will often be met with, in the commencement of the 

 characters of those species to which the individual under examina- 

 tion does not belong. 



FARTHER EXPLANATIONS RELATING TO THE CHARAC- 

 TERISTIC. 



1. Wherever, in the different orders of solid minerals, a break in 

 the series of hardness occurs, it is marked by a line of separation ; 

 and the species in those cases where more than one exists between 

 every two lines, are arranged in the order of their specific gravities. 



2. The minerals contained in the appendices of the orders in the 

 two first classes consist of species concerning whose systems of 

 crystallization our knowledge is yet imperfect ; it is believed how- 

 ever, that they are referred to those orders where the student would 

 most naturally be led to look for them, in a majority of cases. The 

 appendix to the first order in the third class, embraces such miner- 

 als as are yet too imperfectly described to enable us to decide wheth- 

 er they constitute independent species, or coalesce with ethers 

 already known. 



3. At the conclusion of several orders in the first and second clas- 

 ses, references enclosed by a parenthesis, to members of other orders 

 will be observed, the object of which is to indicate to the inquirer, who 

 has run over ineffectually a particular order, in what other order the 

 object of his search may be found. For example, let the mineral be an 

 uncleavable crystal of the form of the regular Octahedron, whose 

 hardness = 25. ..3-0. and whose Specific gravity = 8 -4.. .8-9. Or- 

 der 111 in class I. would first be recurred to : but it would be found 

 impossible to identify it with either of its species. At the end of 

 the order, however, 'reference is made to Species 6, Order I ; by 

 turning to which, we discover an agreement between its character, 

 and the properties of the mineral in question. 



4. The names in small capitals, which are preceded by the sign ?, 

 and whose characters are carried out in parenthesis are not regard- 

 ed by the author as fully entitled to stand as distinct species ; but 

 are conceived to belong to those species which they immediately 

 succeed in the arrangement. 



5. Wherever, among the synonyms, a mark of interrogation fol- 

 lows a name, it is intended to indicate a doubt whether the substan- 

 ces to which it is applied, belong to the species with which such 

 name is arranged. 



