René Just Haüy (French pronunciation: [aɥi]) FRS MWS FRSE (28 February 1743 – 1 June 1822) was a French priest and mineralogist, commonly styled the Abbé Haüy after he was made an honorary canon of Notre Dame. Due to his innovative work on crystal structure and his four-volume Traité de Minéralogie (1801), he is often referred to as the "Father of Modern Crystallography". During the French Revolution he also helped to establish the metric system.
Biography
Early life René-Just Haüy was born at Saint-Just-en-Chaussée on February 28, 1743, in the province of Picardy (later the département of Oise). His parents were Just Haüy, a poor linen-weaver, and Magdeleine Candelot. Haüy's interest in the services and music of the local church brought him to the attention of the prior of a nearby abbey of Premonstrants. Through him, Haüy was introduced to a colleague in Paris and obtained a scholarship to the College of Navarre. Haüy eventually became an usher, and in 1764, was appointed regent (master) of the fourth class. Haüy also progressed in his religious training. He was tonsured in 1762, took minor orders in 1765, was appointed a subdeacon in 1767, became a deacon in 1769, and was ordained as a Roman Catholic priest in 1770. After his ordination, Haüy became regent (teacher) of the second class at the Collège du Cardinal-Lemoine. Through his friendship with his spiritual director, Abbé Lhomond, Haüy became interested first in botany, and after hearing a lecture by Louis-Jean-Marie Daubenton, in mineralogy. His brother Valentin Haüy was the founder of the first school for the blind, the Institution des Jeunes Aveugles (Institute for Blind Youth) in Paris.
Crystallography
An accident apparently directed René-Just Haüy's attention to what became a new field in natural history, crystallography. Haüy was examining a broken specimen of calcareous spar in the collection of Jacques de France de Croisset. (According to some accounts, Haüy dropped the specimen and caused it to break.) He became intrigued by the perfectly smooth plane of the fracture.
"The observation I have just noted is that which has served to develop my ideas on the structure of crystals. It presented itself in the case of a crystal that the citizen Defrance was kind enough to give me just after it had broken off from a group this enlightened amateur was showing me, and which formed part of his mineralogical collection. The prism had a single fracture along one of the edges of the base, by which it had been attached to the rest of the group. Instead of placing it in the collection I was then forming, I tried to divide it in other directions, and I succeeded, after several attempts, in extracting its rhomboid nucleus." René-Just Haüy, Traité de minéralogie (1801)
Studying the fragments inspired Haüy to make further experiments in crystal cutting. Breaking down crystals to the smallest pieces possible, Haüy concluded that each type of crystal has a fundamental primitive, nucleus or “integrant molecule” of a particular shape, that could not be broken further without destroying both the physical and chemical nature of the crystal. He further argued that crystal structures are made up of orderly arrangements of these integrant molecules in successive layers, according to geometrical laws of crystallization. Crystals that had been classed together previously were identified as being of separate mineral species if their fundamental structure differed. Heavyspar, for example, was differentiated into specimens containing barium and strontium. The value of Haüy's discovery was immediately recognized.
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