Leadwoods were Deepwoods trees with extremely heavy wood. They were of the Third Order of Buoyant Wood, and thus their weight remained constant at any temperature. Leadwood lumber was used to in the construction of heavy objects, such as the hull weights of sky ships or the bullets of phraxmuskets and phraxpistols. It was also lightning-resistant, so was often used for roof tiles, such as on Cade's cabin.
In the Edgeworld, lead ore and leadwood lumber existed. Both substances, when refined, produced lead.
The reality of very different things yielding the same substance when processed and refined, such as lead ore and leadwood lumber is exemplified by sugar cane and sugar beet. Both result in granulated sugar.