176 FIRST YEAR COURSE IN GENERAL SCIENCE 



we find that they help to explain some very important and 

 interesting things about our home, the earth. How the 

 rocks were made; where the material came from; why some 

 rocks are under water and some aboye; why some hills are 

 higher than others; why some are rounded and some sharp; 

 why some plateaus are deeply cut and others plain these 

 are a few of the questions that depend, for their answers, on 

 a knowledge of minerals. 



An old proverb says that "A chain is not stronger than 

 its weakest link." We might borrow the form and say that 

 a rock is not more lasting than its softest mineral. The 

 hills are not everlasting, although they remain apparently 

 unchanged for many generations of human life. The dura- 

 bility of the rocks of which they are made depends largely 

 upon the hardness and solubility of the minerals which 

 compose the rocks. 



EXERCISES 



1. Which is more valuable, a gem cut from rock crystal or one made 

 from amethyst? Why? 



2. Asbestos may be woven like thread or made into sheets like 

 paper, but it has a property entirely different from either thread or 

 paper. What is this property? 



3. For what purposes is asbestos cloth or asbestos paper used? 



4. What mineral is a large constituent of volcanic rocks? Why? 



5. The soil on the old slopes of Vesuvius is very fertile. Give a 

 reason, remembering that soil is partly made of decomposed rock. 



6. Why are underground caves never made in granite rock? 



7. Why does it not always prove profitable to take the gold from 

 a vein? 



8. Why cannot quartz, as well as feldspar, be made into pottery? 



9. Give directions for preparing some crystals of salt, or copper 

 sulphate, or alum. 



10. Explain why stalactites show a crystalline structure. 



11. Arrange the following in groups, as rocks or minerals: marble, 

 agate, iron ore, sandstone, calcite, granite, feldspar, limestone, gypsum, 

 quartz, asbestos, amethyst, mica. 



