QUARTZ. FELDSPAR. 39 



of which they are composed are very few, and can 

 be learned by any one in a very short time. 



The most important of these are the following, 

 viz. : 



1. Quartz. 



2. Feldspar. 



3. Mica. 



4. Talc. 



5. Chlorite. 



6. Hornblende. 



7. Serpentine. 



8. Limestone. 



9. Slate and Clay. 



10. Augite. 



1. Quartz is one of the hardest minerals of which 

 rocks are composed, and consists almost entirely 

 of silex. It gives sparks with steel ; breaks into 

 sharp, angular fragments by the blow of a hammer, 

 leaving a smooth, shining surface, like glass. Hence 

 the fracture is called vitreous. Quartz readily 

 scratches glass, and, indeed, most other minerals; 

 it is infusible when unmixed, but with alkalis it 

 melts easily and forms glass. Its colours are va- 

 rious shades of white, gray, brown, yellow, red, and 

 green. When rubbed, it yields a phosphorescent 

 light, and often a peculiar odour. It is not acted 

 on by any acid except the fluoric. Quartz often 

 occurs in a crystallized form. The most common 

 forms of the crystals are six-sided prisms, termina- 

 ted by six-sided pyramids, thus : 

 p- j Quartz sometimes forms large beds, and 

 ' ' even mountains, though it more generally, 

 yy\\ perhaps, exists in veins intersecting other 

 // \ \ rocks. It forms the great bulk of sand- 

 " stones and gravel-beds. There are nu- 

 merous species of quartz, such as flint, 

 opal, chalcedony, carnelion, agate, jasper, 

 k^j II hornstone, garnet, idocrase, stilbite, zeolite, 

 nJsT~7v zoisite, epidote, &c. Most of the precious 

 stones employed by the lapidary for gems 

 are varieties of quartz. 

 Felspar or feldspar* is a very common mineral, 



* Field-spar. German. 



