454 NATURAL HISTORY. 



the Greek wor&ffrapho, I write, in allusion to its extensive 

 use in writing. The more impure variety is good mate- 

 rial (being fire-proof) for manufacturing fire crucibles 

 for diminishing the friction in heavy machinery, and is 

 also used for giving a gloss or polish to stoves and 

 grates. 



FOURTH CLASS. 

 ORES. 



Minerals which contain the heavy metals, either in a 

 pure state or mixed with other substances. 



FIRST ORDER. 



EARTHS CONTAINING METALS. 



Magnetic Iron Ore Magnetite occurs in six-sided 

 or tabular crystals or prisms ; generally massive, but 

 sometimes detached and disseminate ; color iron or grayish 

 black ; lustre metallic ; opaque ; streak black, rough ; 

 strongly magnetic, and contains a great deal of iron. 

 H. = 5.5 to 6.5. G. = 4.5 to 5.2. Occurs in green- 

 stone and serpentine, and is a valuable iron ore, from 

 which the celebrated Swedish iron is made. Found in 

 Tyrol, Styria, etc., in Europe, and in most of the Eastern 

 States, in North America. 



Chrome Iron Stone Chromium seldom occurs in 

 crystals ; mostly solid, granulate, or foliate ; color iron- 

 gray, shading into pitch-black ; luster metallic, opaque, 



