Hauy's wooden crystal model and a crystal of alum, c 1800.

Rene-Just Hauy is one of the fathers of the science of crystallography, the study of the molecular structure of crystals and their clasification into types. In 1781, he apparently dropped some calcite crystals by accident. He noticed that the broken pieces were rhombohedral in form, and when he deliberately broke other calcite crystals, he discovered that they all exhibited the same form, regardles of type and source of the sample. He proposed that all the molecules of calcite have the same form, and that they fit together in a regular pattern to form larger structures. Hauy then went on to suggest that similar principles applied to other minerals and that there were six basic crystal forms on which all mineral structures were based.