John Webster examines a mineral specimen at his worktable.

What makes a stone one particular kind for John Webster?

John Webster (1610–1682), an English physician and naturalist, examines the origins of metals and stones in his Metallographia. A difficulty interests him that one can easily overlook in a collection. Each specimen is already complete when it goes on display and may even have a name attached. Anyone asking how it came into existence has to imagine a time when its material had yet to acquire this particular form.

The material leaves a question open

[…] and in stones there is a petrifying quality, vapour or steam, that doth turn the matter aggregated, into the nature of this or that stone; as in flint, to flint; in greet, or free-stone, to the like.

– John Webster, Metallographia, 1671, p. 46.[1]

Webster distinguishes matter gathering in a place from the property that makes it become a certain kind of stone. For the latter he draws on the language of vapour and exhalation. A vapour can spread and enter small spaces without already having the outline of the solid that will ultimately appear. This freedom of movement makes the image useful to his argument. On such a model a visible outline need not be present in the material from the beginning.

Explaining an individual specimen

The modest expression about this or that stone makes a real difference. To say simply that something grew hard would leave Webster unsatisfied. The same words would apply to a great many unlike specimens. He wants a reason for the particular character of the stone that emerges. His language records an attempt to pass from a general account of change to an explanation of an individual result. A labelled object in a cabinet would be a place to begin that enquiry, with much of its history still to discover.