MINERALOOV. 9 



Magnesium is a metallic element, and it somewhat resem- 

 bles in appearance the metal aluminum. It combines rapidly 

 with oxygen, and when burning it is highly luminous. 

 The light from burning magnesium is used by photogra- 

 phers when making photographic negatives at night. When 

 comVjined with oxygen, it forms magnesia. Combined with 

 sulphuric acid, it forms Epsom salts. In combination with 

 silica and a little iron, it forms the mineral chrysolite, which 

 sometimes exists in great beds of rocks, especially abundant 

 among the mountains of North Carolina. 



Chrysolite in its purest condition forms the beautiful min- 

 eral, olivine, much admired as an ornamental stone. When 

 combined with water (ten or twelve per cent.j it forms the 

 green mineral, serpentine, sometimes called serpentine marble. 

 The most beautiful specimens of this so-called marble are 

 found near Easton, in Pennsylvania, and in Harford County, 

 in Maryland. Serpentine is sometimes found included in 

 limestone. This variety is called verde antique marble. Talc 

 and soapstone are varieties of serpentine. The former is found 

 abundanth' in St. Lawrence County, in New York, in Cher- 

 okee County, in North Carolina, and in an adjoining county 

 in Georgia. When powdered, it is used in adulterating 

 paper, and also as a toilet powder, sometimes called talcum. 



So much time has already been consumed in describing a 

 few of the substances which enter into the composition of 

 some minerals, that there is now only an opportunity for a 

 brief reference to some of the most common and important of 

 these minerals. 



Feldspar is one of the most abundant, as well as one of the 

 most important of minerals. The most common, called ortho- 

 clase, consists of silica, alumina and potash. When decom- 

 posed, it forms the chief portion of the clays of the earth. 

 It supplies two of the substances used in the manufacture of 

 porcelain ware, which consists of quartz, feldspar and the 

 white clay, kaolin. Orthoclase feldspar, when decomposed, 

 affords the chief supj-ily f)f potash for the use of plants. 



