34 New York State Museum 



as hematite which gives a reddish color and limonite 

 which gives a yellowish color. Some rocks are practically 

 devoid of cement. Sandstones show a variety of colors, 

 depending upon the nature of the cement. The common 

 colors are brick-red to reddish brown and brown, buff to 

 dark yellow and white to gray; green, purple and black 

 colors occur more rarely. Iron oxides predominate where 

 the red, brown and yellow colors are found ; the cements 

 are apt to be calcareous or argillaceous where the lighter 

 colors are found. 



Sandstones are porous rocks and they have a granular 

 texture. When a sandstone is broken the fracture takes 

 place chiefly in the cement leaving the grains outstanding 

 and giving a sugary appearance and feeling to the broken 

 surface. Sandstones have been given various names ac- 

 cording to composition and cementing materials. Sand- 

 stones in which quartz prevails are known as quarts sand- 

 stones and these when pure are valuable in glass-making. 

 In some quartz sandstones, where the cement is silica, the 

 silica is precipitated in crystalline form around the angu- 

 lar grains forming crystal sandstone. Quart site is a 

 quartz sandstone in which the grains have been enlarged 

 by deposition of silica until the pores are completely 

 filled and the rock becomes a hard, very resistant mass. 

 Ouartzites are generally regarded as metamorphic rocks. 

 Micaceous sandstones contain muscovite mica. Ferrugi- 

 nous sandstones are those with iron compounds as 

 cements; calcareous sandstones those with carbonate of 

 lime ; argillaceous sandstones those in which clay is pres- 

 ent. Brownstone is a sandstone with iron oxide cement 

 much used for building purposes ; the bluestone or flag- 

 stone used for flags and sidewalk curbings is a highly 

 argillaceous sandstone of even texture and bedding; grit 



