Paracelsus examines a piece of ore beside a stream near a mine

Where minerals take root

Paracelsus (1493/94–1541) was a physician and natural philosopher born in Einsiedeln. To account for the formation of ores he asks his readers to picture a fruit tree. The roots lie in the earth while ripe cherries hang in the air. He imagines minerals crossing a similar boundary.

What the tree reveals

Someone picking a cherry is unlikely to mistake the place of harvest for the place where the roots grow. With an ore vein the inference is more tempting. Finding metal underground seems a good reason to say that earth produced it. It is this inference that Paracelsus questions.[1]

Moreover, as you see, all fruits grow out of the earth into the air, and none of them remain in the earth, but go out of it and separate themselves from it, so, growing out of the water, there go forth metals, salts, gems, stones, talcs, marcasites, sulphurs, etc.—all proceeding from the matrix of this element into another matrix, that is, into the earth, where the water completes its operation, but the root of minerals is in the water, as the root of trees and herbs is in the earth.[1]

An underground harvest

Water occupies the place in his account that soil occupies for the tree. A miner following a vein therefore sees only part of its history. Even the uneven yield of different deposits fits the comparison. One tree bears abundantly while another offers only a few pieces of fruit.[1]