MINERALOGY. 421 



SPECIAL MINERALOGY. 



Whilst Geology considers minerals as dependent rela- 

 tions constituting soils, and treats of their various rocks 

 only as associated in the structure of the earth, it is the 

 object of Special Mineralogy to consider them as inde- 

 pendent bodies, and to describe the individual qualities 

 of the several mineral species, very few of which, al- 

 though daily met with, are to most only known by 

 name. Preliminary to a particular discussion of their 

 characteristic structure or uses, we will remark that 

 they all have in common three peculiar properties, vary- 

 ing, however, very considerably in the different species 

 to which they belong, as exhibited in each individual. 

 The terms by which these properties are distinguished 

 are Fracture, Degree of Hardness, and Specific 

 Gravity. 



By Fracture, which is of several kinds, is meant the 

 appearance of the mineral when broken ; for instance, 

 Conchoidal, when the mineral breaks with a curved and 

 convex or concave surface of fracture, resembling the in- 

 side of a shell ; flint is a good example. Uneven, when 

 the surface of the fracture is rough, with numerous 

 small elevations and depressions. Brittle, when the 

 parts of the mineral separate into powder on attempting 

 to cut it. Even, when the surface of the fracture is 

 nearly or quite flat. Malleable, when slices may be 

 cut off or splintered, and Hackly, when the elevations 

 are sharp or jagged, as in broken iron. 



In order to give a definite character to the results ob- 

 tained with respect to the hardness of minerals, a scale 



