It forms as brown rounded to concretionary masses. It is cloddy, porous and deficient in concretionary materials. Some early vertebrates preserved in the Mazon Creek's concretionary nodules have fossilized soft tissue. Nodular phosphorite, coal fragments and concretionary siderite occur in the coarse beds. These sediments are often cemented into either concretionary masses or beds by calcrete. The specimen was found in a concretionary sandstone lens with the anterior portion eroding out. It also contains conglomerates and some concretionary limestone or calcretes which represent fossil soil horizons. It is a globular, botryoidal or stalactic concretionary form of opal.