SIMPLE MINERALS. 185 



softer, yielding easily to the nail, and has a soapy feel. It 

 includes the varieties, chlorite (which is green), nacrite, 

 green earth, steatite or soapstone, and vermiculite. 



It is composed of silica 62, magnesia 27, oxide of iron 3.5, 

 alumina 1.5, water 6. Nacrite and green earth have from 4 

 to 17 per cent, of potash, and a trace of lime. It appears to 

 be a silicate of magnesia, and of the other bases which are 

 above mentioned. 



Hornblende is a black or brown mineral, exceedingly tough, 

 and. of an earthy appearance when not crystallized. 



It is composed, according to the analysis of Bornsdorf, of 



Protoxide of iron 18.75 



Protoxide of manganese 1.15 



Hydrofluoric acid 0.41 



Water 0.50 



Hence it is a silicate of magnesia, lime, oxide of iron, etc. 



Serpentine. Serpentine is a hard compact mineral, of a 

 resinous or greasy lustre, and of a dark-green or blackish- 

 green color. According to the analysis of Shepherd, it is 

 composed of 



Silica 40.08 I Water 15.67 



Magnesia 41.40 I Protoxide of iron 2.70 



A species from Lynnfield, Mass. analyzed by Dr. C. T. Jack- 

 son, gave silica 37, magnesia 42, oxide of iron 2, water 15. 

 Hence, serpentine is almost wholly a silicate of magnesia. 



Calcareous spar, or carbonate of lime, is well known by the 

 names of marble, chalk, limestone, etc. It assumes a great 

 variety of forms, and may be known by the brisk efferves- 

 cence produced by dropping on to it a few drops of sulphuric 

 acid. It is composed, according to Phillips, of carbonic acid 

 44, lime 55.5. Limestone is found, in great abundance, 

 but it is not always pure. It often contains magnesia, the dolo- 

 mite species ; iron ; the feruginous limestone ; alumina ; and 

 silica. The limestones of Rhode Island, according to the 

 analysis of C. T. Jackson, contain from 50 to 97.6 per centi. 

 16 



