Ferro, cobre, zinco, estanho, ouro e chumbo em Mumford (1934)

If the use of metals came at a relatively late date in technics, the reason is not far to seek. Metals, to begin with, usually exist as compounds in ores; and the ores themselves are often inaccessible, hard to find, and difficult to bring to the surface: even if they lie in the open they are not easy to disengage. Such a common metal as zinc was not discovered till the sixteenth century. The extraction of metals, unlike the cutting down of trees or the digging of flint, requires high temperatures over considerable periods. Even after the metals are [69] extracted they are hard to work: the easiest is one of the most precious, gold, while the hardest is the most useful, iron. In between are tin, lead, copper, the latter of which can be worked cold only in small masses or sheets. In short: the ores and metals are recalcitrant materials: they evade discovery and they resist treatment. Only by being softened do the metals respond: where there is metal there must be fire. (Mumford 1934:68-9)

MUMFORD, Lewis. 1934. Technique and civilization. New York: Harcourt, Brace and Company.