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 
fight, and often a peculiar odour. It is not acted 
on by any acid except the jiuoric. 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, 
yvK perhaps, exists in veins intersecting other 
jCJLX^ rocks. It form? 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, 
NA~f/ 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 mineralf 
* Field-spar. German. 
