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, 



1. Quartz. 



2. Feldspar. 



3. Mica. 



4. Talc. 



.5. Chlorite. 



6. Hornblende. 



7. Serpentine. 



8. Limestone. 



9. Slate and Clay. 



10. Audte. 



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, 

 yvV\ perhaps, exists in veins intersecting other 

 y V \\ rocks. It formes the great bulk of sand- 

 stones and gravel-beds. There are nu- 

 merous species of quartz, such as flint, 

 opal, chalcedony, carnelion, agate, jasper, 

 hornstone, garnet, idocrase, stilbite, zeolite, 

 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, 



* Fiold-spar. German. 



