RENÉ JUST HAÜY (1743 - 1822). Essai d'une Théorie sur la Structure des Crystaux. Paris: Chez Gogué & Née de la Rochelle, 1784.

Born to a poor family, Haüy received a good classical and theological education in Paris. In 1770, after he was ordained a priest, Haüy was assigned a teaching post at the Collège Cardinal Lemoine. There, after attending some lectures on mineralogy, he turned his attention to that discipline, and his success in this field led him to be elected to the Paris Academy of Science in 1783. After nearly being executed during the French revolution for refusing to swear an oath of allegiance to the new regime, in 1795, he was appointed an instructor of physics and mineralogy at the Ècole des Mines (School of Mines), and later became professor of mineralogy at the Muséum d'Histoire Naturelle, where he greatly enlarged the mineral collection. In 1809, Haüy also assumed the newly created chair of mineralogy at the Sorbonne. He retained these posts until his death.

Haüy's first printed book, the Essai, was instrumental in establishing a solid foundation on which modern theories of crystal structure rest. After the introduction, the text is divided into ten articles, the first two of which describe the structure of crystals based upon primary and secondary forms. The next seven articles apply the theory to various minerals, while the final chapter gives observations and conjectures on the formation of crystals.

In the Essai, Haüy brought together the advances in crystallography made by Romé de l'Isle and others into a coherent structural theory, based on the idea that crystals are built up by stacking together a basic structural unit, the "molecule constituante" (later renamed by him to "molecule integrante"). From the idea that a crystal is composed of stacks of identical parallelepipeds, he reasoned that the slope of each macroscopic crystal face must be mathematically related to the shapes of the parallelepipeds and describable by integers corresponding to the number of them that constitute the "rise" over "run" ratio of that face. Haüy also theorized a common "primitive form" for all crystals of the same species, which was often revealed by cleavage of a crystal symmetrically along its angles and edges.

Haüy's contributions throughout his life earned him the title of father of modern crystallography.

Curtis P. Schuh, Mineralogy & Crystallography: An Annotated Bibliography of Books Published 1469 through 1919. Tucson: privately published, 2005, p673-674.

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