Earth Study 



833 



Observations i . Describe your piece of mica. Pull off a layer with the 

 point of your knife. See if you can separate this layer into two layers or 

 more. 



2. Can you see through mica? Can you bend it? Does it break 

 easily? What is the color of your specimen? What is its luster? Can 

 you cut it with a knife ? Can you scratch it with the thumb nail ? What 

 color is the streak left by scratching it with steel ? 



3 . What are some of the uses of mica ? How is it especially fitted for 

 some uses? 



4. Write a theme on how and where mica is obtained. 



GRANITE 



Teacher's Story 



In granite, the quartz may be detected by its fracture, which is always 

 conchoidal and never flat; that is, it has no cleavage planes. It is usually 

 white or smoky, and is glassy in luster. It cannot be scratched with a 

 knife. The feldspar is 

 usually whitish or flesh- 

 colored and the smooth 

 surface of its cleavage 

 planes shines brilliantly 

 as the light strikes upon 

 it; it can be scratched 

 with a knife but this 

 requires effort. The 

 mica is in pearly scales, 

 sometimes whitish and 

 sometimes black. The 

 scales of these mica 

 particles may be lifted 

 off with a knife, and it 

 may thus be distin- 

 guished. If there are 

 black particles in the 

 granite which do not 

 separate, like the mica, 

 into thin layers, they 

 probably consist of 

 hornblende. 



Granite is used ex- 

 tensively for building 

 purposes and for monu- 

 ments. It is a very 

 durable stone but in 

 the northeastern United 

 States where there is 



much rain and cold 

 weather, the stone 

 decays. Mica is the 



The granite obelisk still standing on the site of the ancient 



city of On. 

 Photo by J. H. Comstock. 



