ECONOMIC GEOLOGY 



185 



SANDSTONE 



Sandstone consists of grains of sand which are united by a 



cement. 



The grains may be of varying sizes, from almost impalpable 

 dust to small pebbles, and may be angular or more or less rounded 

 in form. The cementing matter also may vary greatly in its 

 nature. From this variation, both in the grains and in the 

 cement, there is an almost endless gradation in the kinds of sand- 

 stone. 



Quartz is the essential constituent, but with it there may be 

 feldspar, mica, calcite, pyrite, glauconite, clay or other minerals, 

 and rock fragments common to stone of sedimentary origin. 

 These accessory materials often give character to the mass, and 

 make a basis for a division into feldspathic, micaceous, calcare- 

 ous sandstones, etc.. as one or another of them predominates. 



The texture of the mass also is subject to a wide range of vari- 

 ation, from fine-grained, almost aphanitic, to pebbly sandstone, 

 or conglomerate, or a brecciated stone in which the component 

 parts are more or less angular. 



Some of the brown sandstones of the Triassic age, quarried 

 near Haverstraw, are such conglomeratic and brecciated sand- 

 stones. Accordingly, as the grains are small or large, the stone 

 is said to be fine-grained or coarse-grained. 



The variety of the cementing material also affords a basis for 

 classification. Silicious sandstones have the grains bound to- 

 gether by silica. They consist almost exclusively of quartz, 

 and grade into quartzite. The ferruginous varieties have for 

 their cement an oxide of iron, often coating the grains and mak- 

 ing a considerable percentage of the whole. The iron is usually 

 present as ferric oxide. Calcareous sandstones are marked by 

 the presence of carbonate of lime. When it exceeds the quartz 

 in amount, the sandstone becomes a silicious limestone. In the 

 argillaceous varieties, the binding material is a clay, or an im- 

 pure kaolin. 



The cementing material determines in most cases the color. 

 The various shades of red and yellow depend upon the iron 



