.207. PHYSICAL PROPERTIES Olr MINERALS. 299 



ferred from the consideration, that these properties refer 

 to the minerals themselves, even though we should ab- 

 stract from their geometrical and optical properties. 



. 207. STATE OF AGGREGATION. 



In respect to the state of aggregation, we distin- 

 guish solid and fluid minerals. The former are 

 either brittle, or sectile, or malleable, or flexible, or 

 elastic ; the latter are either liquid or expansible. 



A solid mineral is said to be . 



1, Brittle, if in the experiment of detaching small par- 

 tides of it with a knife or a file, these particles lose their 

 coherence, and separate with a grating noise, while they fly 

 about in the state of powder. The particles therefore cannot 

 alter their respective sitviations without separating en- 

 tirely. Ex. All the species cf the orders Gem, Spar, Py- 

 rites, several of those of Ore, Haloide, &c. 



2, Malleable, if the particles detached by the knife, do 

 not lose their connexion. From a malleable mineral, we 

 may detach slices as we do from metallic lead. Ex. Many 

 metals, hexahedral Pearl-kerate, hexahedral Silver-glance, 

 and several varieties of black Mineral-resin. 



3, Sectile, if in the above experiment the particles lose 

 their connexion, and do not allow the separation of any 

 slices ; but if at the same time they do not fly about with 

 a noise, but quietly remain upon the instrument we have 

 applied. The sectile minerals form an intermediate stage 

 between the malleable and the brittle ones. This state of 

 aggregation is commonly not distinguished by natural philo- 

 sophers, though it is very useful in the characters of several 

 species. Examples of sectile minerals we have in most of 

 the species of the orders Mica and Glance, in some of the 

 orders Haloide, Baryte, &c. 



4, Ductile, if it can be wrought into Sheets or wire; so 

 that by the application of a greater or lesser force, the par* 



