Sometimes ironstone hosts concretions or opal gems. Boulder opal consists of concretions and fracture fillings in a dark siliceous ironstone matrix. Chert, ironstone and calcareous deposits occur in small amounts. It grows in sandy, peaty or clay soils around sandstone or ironstone. Onondaga Pottery began producing a heavy earthenware called "Ironstone" but struggled to succeed. The popularity of Spode's ironstone surpassed the traditional faience pottery in France. Heavy clay and Ironstone deposits surround Banbury. It is built of coursed ironstone and cobblestones with ashlar dressings. These are magnetite, titanomagnetite, massive hematite and pisolitic ironstone deposits. The Stanton Ironworks acquired a number of smaller ironstone quarrying and ironworks companies. Between 1856 and 1926 high-grade magnetic ironstone was mined in Rosedale. The walls are of red and blue brick with ironstone dressings. The geology is the coal measures containing coal and ironstone. In the north of the county a large ironstone quarrying industry developed from 1850. Molybdenum may be strongly sorbed in ironstone soils.