Earthy mixture of fine-grained minerals, which range widely in composition.
bivalves , or as powder mixed with clay and silica-containing silt. Large deposits contain 80–90% calcium carbonate and less than 3% magnesium carbonate. With decreasing amounts of lime, calcium-containing marls are called clays and clayey limestones. Marls rich in {{link=potash">potash (potassium carbonate), called greensand marls, are used as water softeners. Marls have also been used in the manufacture of insulating material and portland cement , as liming material, and in making bricks.