832 Handbook of Nature-Study 



Observations i. What is the shape of the feldspar crystal? 



2. What colors are your specimens of feldspar? How many kinds 

 have you ? 



3. What is the luster of feldspar ? 



4. Can you scratch feldspar with the point of a knife? Can you 

 scratch it with quartz? Can you scratch glass with it? 



5. When you scratch feldspar with steel what is the color of the streak 

 left upon it ? 



6. If feldspar is broken, does it break along certain lines, leaving 

 smooth faces ? At what angles do these smooth faces stand to each other ? 



7. How can you tell feldspar from quartz? Write a comparison of 

 feldspar and quartz, giving clearly the characteristics of both. 



8. Hunt over the pebbles found in a sand-bank. Which ones are 

 quartz? Do you find any of feldspar? 



9. When there is so much more feldspar than quartz in the earth's 

 crust, why is there so much more quartz than feldspar in sand? 



MICA 



Teacher's Story 



The mica crystal when perfect is a flat crystal with six straight edges. 

 These crystals separate in thin layers parallel with the base. In color mica 

 varies, through shades of brown, from a pale smoked pearl to black. Its 

 luster is pearly, and it can be scratched with the thumb nail. Its distin- 

 guishing characteristic is that the thin layers into which it splits bend with- 

 out breaking and endure great heat. 



Mica was used in antiquity for windows. Because it is transparent and 

 not affected by heat, it is used in the doors of stoves and furnaces and for 

 lamp chimneys. Its strength makes it of use for automobile goggles. 

 Diamond dust is powdered mica, as is also the artificial snow scattered 

 over cotton batting for the decoration of Christmas trees. When ground 

 finely, it is used as an absorbent for nitroglycerine in the manufacture of 

 dynamite 



Mica mines are scarce in this country. There is an interesting one in 

 North Carolina which had evidently been worked centuries before the 

 advent of the white man in America. There are other mica mines in New 

 Hampshire and Canada. The entire production of this mineral in the 

 United States for the year 1908, was valued at a little more than a quarter 

 of a million dollars. Nearly all of this output was used in the electrical 

 industries, since mica is one of the best insulating materials known. 



LESSON CCXVI 



MICA 



_ Leading thought Mica is a crystal which flakes off in thin scales parallel 

 with the base of the crystal. We rarely see a complete mica crystal but 

 simply the thin plates which have split off. The ordinary mica is light 

 colored, but there is a black form. 



^ Method If it is not possible to obtain a mica crystal, get a thick piece of 

 mica which the pupils may split off into layers. 



