PHYSICAL PROPERTIES OF MINERALS. 115 



THE PHYSICAL PROPERTIES OF MINERALS. 



. 97. STATE OF AGGREGATION. 



In respect to the mode of aggregation, minerals, in the 

 first place, are either solid or fluid. 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 detaching small particles of it with a knife or a 

 file, these particles lose their coherence, and separate with a gia- 

 ting noise, in a powder. Ex. Quartz, Feldspar and Iron Pyrites. 



2. Malleable, if the particles detached by the knife do not lose 

 their connexion, but rather separate in slices. Ex. Native Silver, 

 Native Gold and Native Copper. 



3. Sectilc, if the particles, on their separation, as above, merely 

 lose their connexion, without flying off in powder. Sectile miner- 

 als are intermediate between brittle and malleable minerals. Ex. 

 Talc and Gypsum. 



4. Ductile, if it can be wrought into sheets or wire ; so that, by 

 the application of a greater or less force, the particles of the mineral 

 may change their relative situation, without absolutely losing their 

 connexion. Ex. Native Gold and Native Silver. 



5. Flexible, when the particles allow of being bent in different 

 directions without breaking, and remain in the direction in which 

 they have been bent. Ex. Talc and Sulphuret of Molybdena. 



6. Elastic, if the particles on being bent out of their natural po- 

 sition, resume their former situation when the disturbing force is 

 removed. Ex. Mica. 



A fluid is more particularly said to be, 



1. Liquid, if in pouring it out from a vessel, perfectly round drops 

 are formed. Ex. Water and Mercury. 



2. Viscid, if the drops are not round, but ropy. Ex. Petroleum. 

 Expansible minerals do not shew any difference in these respects. 



They comprehend the Gases and some of the Acids. 



It is evident that all these properties are subject to slight variations, 

 and that they must pass into each other by insensible gradations. 



