36 THE NEW METHOD 



which are oxygen, the most abundant of all the sev- 

 enty elements, silicon, the next most abundant after 

 oxygen. These two elements make up three-quarters 

 of the weight of feldspar, and two remarkable metals 

 make up the other quarter. 



" Another way of stating this, as we do when we 

 work problems in arithmetic about this mineral, after 

 we see our specimens weighed, is this : In one hun- 

 dred grains of pure feldspar there are 46 grains of 

 oxygen, 30 grains of silicon, 14 grains of potassium, 

 and 10 grains of aluminum. Then in one pound, or 

 seventy hundred grains, there are seventy times these 

 numbers, and the oxygen is 3220 grains, silicon 2100 

 grains, potassium 980 grains, and aluminum 700 

 grains. All these parts added make the whole, or 

 7000 grains. 



' ' When feldspar is broken the break follows the 

 cleavage planes which run through it in two direc- 

 tions which are at right angles to each other. These 

 planes have a bright pearly luster. Feldspar is not 

 quite as hard as quartz. Its degree of hardness is six, 

 and quartz is seven, and the diamond is ten, which is 

 the hardest thing in the world. Talc is the softest of 

 all minerals. Its degree is one in a scale from one to 

 ten. Feldspar is slowly ground by natural processes, 

 and converted into clay, which is made into pottery, 

 and the finest of it into porcelain, another name for 



