Commercial sandstone is a lithified sand that chiefly comprises quartz or quartz and
feldspar with a fragmental (clastic) texture. Sandstone contains interstitial cementing
materials, such as calcite, clay, iron oxides, or silica. Arkose (abundant feldspar
grains), graywacke (abundant angular rock fragments), and conglomerate (abundant rounded
rock fragments) are included in this category. Other members of this category include
bluestone, which is a dense, hard, fine-grained feldspathic sandstone that splits
easily along planes into thin, smooth slabs; brownstone, which can be sawn or split,
is a feldspathic sandstone of brown to reddish-brown color owing to abundant iron
oxide; and flagstone, which is a sandstone, or sandy slate, typically red, tan or
gray, that splits into large, thin slabs.
