KINDS OF ROCKS. 83 



Pyrophyllite Rook or Schist. — Like the preceding in appearance and soapy- 

 feel, but having the composition of pyrophyllite ($ 67). The color is white and 

 gray, or greenish white. Occurs in North Carolina; one of the varieties from 

 the Deep River region is used for slate-pencils. 



6. Quartzose rocks. 



88. (1.) Qttartzite, or Granular Quartz Rock. — A very hard, com- 

 pact rock, consisting of quartz grains or sand, and usually either 

 white, gray, or grayish red in color. Sometimes contains dissemi- 

 nated scales of feldspar, mica, or talc, and in that case is often 

 laminated or schistose. It is but a step removed from ordinary 

 sandstone, and owes its peculiarities only to a process of consolid- 

 ation. 



(2.) Siliceous Schist. — A schistose, flinty quartz rock, not distinctly gra- 

 nular in texture. 



(3.) Arkose. — A quartz rock, containing much crystallized orthoclase dis- 

 seminated through it. Occurs in the Vosges. 



(4.) Itacolumite. — A schistose quartz rock, consisting of quartz grains with 

 talc or mica. On account of the talc or mica in the lamination, the finer kind 

 is sometimes flexible, and is called flexible sandstone. Occurs often in gold- 

 regions associated with talcose slates. 



(5.) Jasper Rock. — A flinty siliceous rock, of dull red, yellow, or green 

 color, or some other dark shade, breaking with a smooth surface like flint. It 

 consists of quartz, with more or less clay and oxyd of iron. The red contains 

 the oxyd of iron in an anhydrous state, the yellow in a hydrous : on burning 

 the latter it turns red. 



A dull-green chert (or impure flinty siliceous rock) from Cap Rouge, Canada, 

 afforded T. S. Hunt (Logan's Report for 1853-56)— Silica, 77.50, alumina, 8.50, 

 protoxyd of iron, 2.70, lime, 0.73, magnesia, 2.35, soda, 1.38, potash, 1.66, loss by 

 ignition, 4.40 = 99.22. Part of the silica, — nearly 21 per cent. — was in the con- 

 dition of opal. 



(6.) Buhrstone. — A cellular siliceous rock, flinty in texture. It is used 

 for millstones. Found mostly in connection with Tertiary rocks, and formed 

 apparently from the action of siliceous solutions on pre-existing fossili- 

 ferous beds. 



7. Iron-Ore rocks. 



89. Specular Iron-Ore (Hematite) and Magnetic Iron-Ore occur as 

 rocks of considerable thickness among the metamorphic rocks, espe- 

 cially the hornblendic and chloritic kinds. There are schistose or 

 laminated as well as massive varieties. These iron-ore beds occur 

 extensively in northern New York, Canada, Michigan, and Mis- 

 souri ; also in Sweden and elsewhere. Their alternation with chlo- 

 ritic and other schists and gneissoid rocks shows that they are meta- 



