Sandstones are composed of grains of sand that have been cemented together through the aid of heat and pressure, forming a solid rock. The cementing material usually is either silica, carbonate of lime, or an iron oxide. Upon the character of this cementing material is dependent, to a considerable extent, the color of the rock and its adaptability to architectural purposes. If silica alone is present, the rock is of a light color and frequently so hard that it can be worked only with great difficulty. Such stones are among the most durable of all rock, but their light color and poor working qualities are a drawback to their extensive use. Rocks in which carbonate of lime is the cementing material are frequently too soft, crumbling and disintegrating rapidly when exposed to the weather. For many reasons the rocks containing ferruginous cement (iron oxide) are preferable. They are neither too hard to work readily, nor liable to unfavorable alteration when exposed to atmospheric agencies. These rocks usually have a brown or reddish color.

Sandstones are of a great variety of colors, which, as has already been stated, is largely due to the iron contained in them. In texture, sandstones vary widely - from a stone of very fine grain, to one in which the individual grains are the size of a pea. Nearly all sandstones are more or less porous, and hence permeable to a certain extent by water and moisture. Sandstones absorb water most readily in the direction of their lamination or grain. The strength and hardness of sandstones vary between wide limits. Most of the varieties are easily worked, and split evenly. The formations of sandstone in the United States are very extensive. The crushing strength of sandstone varies widely, being from 2,500 pounds to 13,500 pounds per square inch, and specimens have been obtained that require a load of 29,270 pounds per square inch to crush them.