FRACTURE. 65 



feldspar, but with more difficulty than apatite, its hardness ia 

 described as 5£ or 5*5. 



The file should be run across the mineral three or four 

 times, and care should be taken to make the trial on angles 

 equally blunt, and on parts of the specimen not altered bj 

 exposure. Trials should also be made by scratching the 

 specimen under examination with the minerals in the above 

 scale, as sometimes, owing to a loose aggregation of particles, 

 the file wears down the specimen rapidly, although the par 

 tides are very hard. 



STATE OF AGGREGATION. 



Solid minerals may be either brittle, sectile, malleable, 

 flexible or elastic. Fluids are either gaseous or liquid. 



1. Brittle : when parts of the mineral separate in powder 

 on attempting to cut it. 



2. Sectile : when thin pieces may be cut off with a knife 

 but the mineral pulverises under a hammer. 



3. Malleable : when slices may be cut off, and these slices 

 will flatten out under the hammer. Example, native gold 

 and silver. 



4. Flexible : when the mineral will bend, and remain bent 

 after the bending force is removed. Example, talc. 



5. Elastic : when after being bent, it will spring back to 

 its original position. Example, mica. 



A liquid is said to be viscous, when on pouring it the drops 

 lengthen and appear ropy. Example, petroleum. 



FRACTURE. 



The following are the several kinds of fracture in minerals : 



1. Conchoidal : when the mineral breaks with a curved, 

 or concave and convex surface of fracture. The word con- 

 choidal is from the Latin concha, a shell. Flint is a good 

 example. 



2. Even : when the surface of fracture is nearly or quite 

 flat. 



3. Uneven : when the surface of fracture is rough with 

 numerous small elevations and depressions. 



4. Hackly : when the elevations are sharp or jagged, as 

 in broken iron. 



Explain the use of the term brittle ; sectile ; malleable, &c. Explain 

 the use of the term conchoidal ; even ; uneven. 



6* 



