clay ironstone
clay ironstone
A compact hard, dark, gray or brown, fine-grained sedimentary rock consisting of a mixture of argillaceous material (up to 30%) and iron carbonate (siderite), occurring in layers of nodules or concretions or as relatively continuous irregular thin beds, and usually associated with carbonaceous strata, esp. overlying a coal seam in the coal measures of the United States or Great Britain; a clayey iron carbonate, or an impure siderite ore occurring admixed with clays. The term has also been applied to an argillaceous rock containing iron oxide (such as hematite or limonite).
A sideritic concretion or nodule occurring in clay ironstone and other argillaceous rocks, often displaying septarian structure.
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