The science of crystallography — from the Greek κρύσταλλος, ice — emerged as a formal discipline in the late eighteenth century, when Romé de l'Isle demonstrated that corresponding angles between faces of the same mineral species are always equal, regardless of specimen size. This law of constancy of interfacial angles became the first quantitative law of mineralogy.

What Romé de l'Isle observed and what Haüy explained — that crystals are built from identical repeating units — anticipated by a century the atomic theory that would vindicate it. The external symmetry of a crystal is a direct expression of the internal symmetry of its lattice. Form is not imposed upon matter; form emerges from it.

This correspondence between visible form and invisible structure is the central philosophical claim of crystallography, and it extends beyond mineral science into a broader Victorian epistemology: that careful observation of surfaces can yield knowledge of depths. The geologist reading strata, the botanist reading leaf venation, the philologist reading word roots — all are engaged in the same hermeneutic project that the mineralogist pursues in reading crystal faces.

The cabinet of curiosities — that peculiarly early-modern institution — was built on exactly this faith. To collect specimens was to read them, to read them was to understand the laws governing their formation, and to understand those laws was to understand something of the mind that authored them.