Greensand
Greensand is an olive-green coloured sandstone rock which found in narrow bands, particularly associated with bands of chalk and clay in northern and western Europe. Greensand contains grains of the mineral glauconite, an iron potassium silicate with very low resistance.
Most greensand formations were deposited in marine environments during the Jurassic and Cretaceous periods.
Greensand is a common ingredient in garden fertilisers. It is also used directly in organic gardening and organic farming.
See also: Cambridge Greensand, Upper Greensand.