takkI COMMOX rocks 41 



The color of the nietamorphic rocks vary as widely as the 

 igneous rocks. The gneisses usually have colors similar to the 

 granites, etc., from which they have been derived. If there is 

 an abundance of the dark minerals the rock is dark gray, or 

 sometimes it is greenish, or nearly black if the dark mineral is 

 biotite. The schists are light-colored also, if the predominating 

 mineral is light colored. This is especially true of those schists 

 which contain a large amount of white mica. ]\Iany schists are 

 ijreenish in color and still others are almost black. 



Schists and gneisses ma}- be given a more specific name if it 

 is so desired. If some mineral is very abundant in the rock the 

 name of this mineral may be prefixed to that of the rock, thus : 

 garnet-gneiss, or hornblende-gneiss, or biotite-gneiss, etc. Simi- 

 lar names are applied to the schists. If tw'o minerals are abund- 

 ant then both names are used, as, biotite-muscovite-gneiss. 



The soils that are derived from the nietamorphic rocks vary 

 as widely as the nature of the rocks from wdiicli they themselves 

 have been derived. \'ery frequently the gravel in the streams 

 which flow from gneisses and schists contain many of the harder 

 minerals that were in them, such as garnets, magnetite, etc. 



When limestone is metamorphosed it becomes marble. The 

 change that takes place is not a change of material, but is a 

 rearrangement of the material already there ; thus larger crystals 

 of calcite (for limestone is composed of calcite) are formed. 

 This is what gives the coarse texture to many marbles, although 

 the texture of marbles varies from very fine to very coarse. 

 When the original limestone is very impure then the resulting 

 marble will contain many minerals as impurities. These usually 

 make the stone unfit for use. A great deal of the marble pro- 

 duced in the United States is quarried in Vermont, but it is also 

 found in ]\Iassachusetts, ■Maryland, New York, Georgia, Cali- 

 fornia, Colorado, and many other states. ]\Iarbles are easy to 

 distinguish because they are crystalline, easily scratched with a 

 knife and efifervesce with acids. 



Ouartzite is formed by a sandstone being cemented with 

 silica. It is a very hard, dense rock, having various colors. It 

 can be distinguished from a sandstone by the fact that it breaks 

 through the grains of which it is composed while in a sandstone 

 the break is around the grains. Ouartzites are ver}' common 

 and are found in nearlv all the states. The Indians used quartzite 

 sometimes to make their arrow heads. 



Slate is a rock that has a very remarkable cleavage so that 

 it splits easily into very thin, large sheets. It is a dense, fine- 



