Historical reference: Do not rely on this information. It is very old. About this collection
Clay Iron Stone, an impure carbonate of iron, containing considerable quantities of clay, which is largely employed for the production of iron; the greater quantity of the metal smelted in England being obtained from this ore. It is of a light to dark-brown colour, sometimes black owing to carbonaceous matter (black band), and occurs largely in the clay and shales of the coal measures.