"Angular Stones": The Birth of Crystallography

Clockwise from top: De Boodt, Kepler, Steno, Hooke, Huyghens
During the Renaissance, a discussion began: do crystals stem from the growth of inert matter or are they somehow sculpted? Using his observations of the shape of quartz crystals, Steno, in the 17th century, was one of the first to imagine crystal growth. It was only during the 18th century, however, that 'crystallographers' formed a picture of the internal structure of crystals by focussing on their external geometry.
It was the discovery of the "constancy of the angles" between the various faces of a given type of crystal, which first drove scientists to suggest that crystals must be made out of a stack of basic building blocks or bricks. This model allowed them to explain crystal faceting. The works of Steno, Romé de L’Isle and Haüy and numerous other scientists thereby gave rise to the new science of "crystallography".
In the 19th century, German and French researchers introduced the concept of symmetry to classify crystals. They used mathematics to formalize their classification theory. Thus, by the beginning of the 20th century, even without being able to "see into" a crystal, crystallographers had developed the notion of atomic order and periodic repetition to understand both the external form of crystals as well as their symmetry.
Romé de l'Isle
© Musée Baron Martin
René Just Haüy
© Ecole des Mines de Paris
Details of the growth forms of fluorite crystals.
© Grenoble Natural History Museum