Cement

Cement manufacture requires argillaceous or shaly limestone; the essential combination is aluminum oxide (alumina and aluminates), silicon oxide (silica and silicates), and calcium oxide (lime). The Jacksonburg formation of Ordovician age (roughly 470 Ma) that divides the limestone terranes of the southern band of the Lehigh Valley and the shale and slate terranes of the northern band has historically been an important source of ‘cement rock.’ In recent years, other limestones with low magnesium content have been used for the cement industry, with alumina and silica added from other sources.