Asphaltic sandstone is a sandstone impregnated with a bituminous residue from the evaporation of petroleum which once occupied the pores of the rock. It has been reported from more than a dozen counties in western Missouri, but the most extensive deposits are probably in Barton, Vernon, and Lafayette counties.
Attention has been directed to the origin of sandstones from ocean deposits of sand and from sand dunes, but it should be recognized also that river channels and stream valleys which contain deposits of sand (such as those on floodplains, river bottoms, and sand bars) may be covered, and the sand consolidated to sandstone. Many years ago, even long ago geologically, a large river, almost comparable in size to the Missouri river, occupied a channel which is now represented by a long narrow sandstone deposit extending from a little north of Clinton through Warrensburg to Lexington and then east through Moberly almost to Paris. Smaller channel sandstones are abundant in other areas in Missouri.
The sandstones of the so-called Roubidoux formation, which occurs in south central Missouri, commonly show well-preserved ripple marks on the rock slabs. These marks were formed exactly as their name suggests—in sand which was thrown into ripples by the shallow water in which it accumulated and was covered and cemented so as to retain the ripple forms.
Ripple marks in limy sandstone.
Sandstone is used for building stone, walks, grindstones, furnace linings, and rock gardens. Large quantities are mined each year near Pacific, Festus and Crystal City, Klondike, and Hermann, for the manufacture of glass and other uses. Common glass is a cooled melt of relatively pure silica sand, soda ash, and lime. Asphaltic sandstone is used in road building. Sand-lime brick are made of sand. Sand is used as a molding material for metal castings, a parting substance between brick in kilns, and in large quantities in concrete and mortar mixtures.
Chert, Flint
The names chert and flint have in some regions been used for the same hard, fine-grained rock found so abundantly in Missouri, but correct usage employs chert for the white and gray varieties, and flint for the black variety. Flint may be thought of as slightly impure chert, a chert which is colored black by a small amount of pigment, usually fine carbon, or perhaps iron sulphide, scattered through it like fine dust.
Chert, fossiliferous and slightly speckled. Note typical sharp edges, smooth surfaces, and conchoidal fracture. From near Columbia.