Sandstone

Sandstone is a rock formed of compacted, and more or less indurated sand. The grains generally consist of quartz, though other mineral substances are often mixed with this; they are colourless, or of a dull white, yellow, brown, red, or green colour. The grains vary in size, forming, as the case may be, a fine or coarse grained stone. The loose sand becomes solidified by pressure simply, but generally there is some binding material present, as argilaceous matter; or the grains may have become cemented by infiltrating water, carrying with it carbonate of lime, or silica, or ferric oxide. The colour of the rock is often due to the cement. Highly indurated sandstones often pass into Quartzite. See the classification at PETROGRAPHY; also OLD RED SANDSTONE.