4 MINERALS AND GEOLOGY 



A. -PHYSICAL CHARACTERS OR PROPERTIES. 



The physical properties of minerals are somewhat numerous ; but 

 many, although of the highest interest in indicating the existence of 

 natural laws, and in their relations to physical science generally, are 

 not readily available as a means of mineral discrimination. These, 

 consequently, will be omitted from consideration in the following 

 pages ; and the other characters will be discussed only in so far as 

 they admit of direct application to the end in view namely, the 

 practical discrimination of minerals one from another.* 



The following are the characters in question : 



1. ASPECT OR LUSTRE. 



2. COLOUR. 



3. STREAK. 



4. FORM. 



5. STRUCTURE. 



6. HARDNESS. 



7. SPECIFIC GRAVITY. 



8. RELATIVE MALLEABILITY. 



9. MAGNETISM. 

 10. TASTE. 



Aspect or Lustre. In reference to this character we have to con- 

 sider first, the kind, and, secondly, the degree or intensity of lustre, 

 as possessed by the mineral under examination. The kind of lustre 

 may be either metallic, as that of a piece of copper, silver, &c. ; or 

 sub-metallic, as that of most kinds of anthracite coal ; or non-metallic, 

 as that of stones in general. Of the non-metallic there are several 

 varieties, as, more especially : the adamantine lustre or that of the 



* Viewed collectively, the Physical Characters of Minerals may be arranged for the purposes 

 of study, under six groups, as follows : 



FIRST GROUP : Morphological Characters : 1, Form. 2, Surface-condition. 3, Structure. 

 4, Cleavage. 5, Fracture. 



SECOND GROUP -.Optical Characters : 1, Aspect or Kind of Lustre. 2, Degree of Lustre. 



3, Colour. 4, Streak. 5, Degree of Transparency. 6, Refraction. 7, Polarization. 

 THIRD GKOUP -.Cohesion Characters : 1, Hardness. 2, Tenacity. 3, Malleability. 4, Ex- 

 pansibility. 



FOURTH GROUP: Sensationary Characters: 1, Weight (Specific Gravity). 2, Feel. 3, Taste, 



4, Odour. 5. Sound. 



FIFTH GROUP : Physical Characters, proper : 1, Magnetism. 2, Electricity. 3, Phos- 

 phorescence. 



SIXTH GROUP : Epigenic Characters : 1, Tarnish. 2, Ordinary Disintegration and Decom- 

 position. 3, Efflorescence. 4, Deliquescence. 



