Pisolith - A Pisolite Is A Sedimentary Rock Made Of Pisoids, Which Are Concretionary Grains - Often Of Calcium Carbonate, But Sometimes Of Rarer Minerals - Which Resemble Ooids But Are Always More Than 2 Mm In Diameter. These Grains Are Approximately Spherical And Have Concentric Layers Reaching 10 Mm In Diameter. Rare Pisolite Samples Found In Abandoned Quarry In Sardinia. Photo