In some parts of Illinois occur sands or sandstone that contain numerous
grains of the green mineral glauconite. If the sands are not discolored
by iron compounds or other substances, they too have a greenish color
and, therefore, are called greensands. Glauconite varies in composition
but contains potassium, magnesium, iron, aluminum, silicon, and water.
Greensand is said to be used in relatively small amounts as a soil
conditioner and as a water-softening agent.
Greensand is known to occur in the general vicinity of Olmsted in
southern Illinois. Near Oregon in northern Illinois an old quarry
exposed 10 feet of greenish brown sandstone that contains glauconite.
Samples from southern Illinois and from the sandstone at Oregon
contained more than 6 percent potassium oxide.