OF EDUCATION 85 



is nine, the hardest mineral we have ever studied. 

 It is of a beautiful pink color of different shades, the 

 larger ones being of a deeper color than the smaller 

 ones. 



" Ruby sapphire is composed of oxygen, aluminum 

 and chromium. In one hundred grains of ruby there 

 are fifty-three grains of aluminum, forty-six and one- 

 half of oxygen, and one-half a grain of chromium, 

 which gives it the color. All the varieties of sapphire 

 have the same composition, and are all colored with 

 chromium, giving sometimes a green color, then 

 called emerald sapphire, sometimes a yellow color, 

 then called topaz sapphire, sometimes of a blue color, 

 the sapphire itself, and sometimes of a purple or 

 violet color, called amethyst sapphire. The emerald 

 sapphire is so rare that it is rarely seen, but still it is 

 not so expensive as the ruby sapphire, the most ex- 

 pensive of all the varieties. It crystallizes in rhom- 

 bohedrons, variously modified. The difference in 

 color in the different varieties of sapphire is accord- 

 ing to the quantity of chromium. Aluminum is a 

 very beautiful silvery metal, very light, and easily 

 bent. If we should burn it in oxygen, which. is very 

 difficult to do, the ashes, or remaining portion, would 

 be the same substance as ruby sapphire. Oxygen is 

 a very useful invisible gas, which sustains fire, keeps 

 all animals alive, and is in a great many different 



