298 TERMINOLOGY. . 206. 



transparency, that this property becomes almost entirely 

 useless in the Determinative part of Natural History. 

 The best employment to be made of it seems to be, in the 

 distinction of compound varieties from simple ones, if the 

 minuteness of the particles of composition prevents them 

 from being observed immediately. Commonly in the same 

 species (. 190.) the compound varieties possess a less 

 degree of transparency than the simple ones. A very dis- 

 tinct example of this we have in the varieties of rhombo- 

 hedral Quartz. Almost all its single individuals, provided 

 they are not impure, shew higher degrees of transparency 

 than flint, hornstone, calcedony, and other compound va- 

 rieties. 



CHAPTER II. 



OF THE PHYSICAL PROPERTIES OF MINERALS. 

 . 206. EXPLANATION. 



The properties of the substance of minerals, or 

 those which have by preference been termed their 

 physical properties, comprehend all those which 

 neither depend upon their form and the space 

 which they fill up, nor upon the presence or ab- 

 sence of light. 



Among these are the State of Aggregation, Hardness, 

 fic Gravity, Magnetism, Electricity, Taste, and Odour. 



It is almost unnecessary to observe, that the expressions 

 mass, or substance, must not be conceived in the chemical 

 sense of the word, and that these properties are not meant to 

 be more essential to the minerals than any of those which 

 have been considered above, which perhaps might be in 



