Entry 01: Haüy's Theory of Crystal Structure
1. About Haüy
Abbé René Just Haüy was born on February 28th, 1743 in a small market town in France. At early age, he studied ancient language and physics at the College of Navarre in Paris. Later, he was transferred to Cardinal Lemoine Collage, where he met and became the friend of Abbé Charles Lhomond (1727–1794), a distinguished botanist. Under the influence of Lhomond, Haüy began the study of botany and become proficient in the field.
During his botany study, he frequently visited Jardin du Roi, where by chance he attended a lecture on mineralogy by Daubenton. He soon realized the lack of system in mineral classification as compared to the systematic classification of plant forms. Then, an accidental break of a friend's calcite crystal let Haüy to discover the rhombic fragment, which marks the beginning of his study of the mathematical relationship between different crystal forms. In 1781, he read his first memoir before the French Academy of Science. And in 1783 he was elected to the Academy. In 1801, his most famous work Traité de minéralogie was published, which became the foundation of crystallography.
Haüy passed away on June 3rd, 1822.
Fig. 1. Portait of Haüy
2. Significance of Haüy's work
There are two most important laws in crystallography: the Law of Constant Interfacial Angles and the Law of Rational Intercepts (Indices), the latter of which was discovered by Haüy.
J. B. L. Romé de l'Isle (1736—1790), another important figure in the history of crystallography, believed that arbitrary truncations could be performed on a primitive form to generate a secondary form, resulting infinite number of possible secondary forms. By establishing the mathematical relationship between the primitive and secondary forms, Haüy indicated that only a limited number of secondary forms would be valid.
Comments on Haüy's work from some historical scientists are collected below:
"He has made of mineralogy a science just as precise and just as methodical as astronomy...In a word we may say that Haüy to Werner and Romé de l'Isle what Newton was to Kepler and Copernicus." — Georges Cuvier (1769 —1832).
"From the moment that the genius Haüy discovered the general fact that they (crystals) could be cloven or split in such directions as to lay bare their peculiar primitive or fundamental forms, from that moment mineralogy ceased to be an unmeaning list of names, a mere laborious cataloging of stones and rubbish." — Sir John Herschel (1792—1871).
"The science of crystallography was entirely created by Haüy's genius, and his successors have had little to do except to perfect the details of his work. No other branch of human knowledge is in the same degree the work of one man alone." — François Mallard (1833—1894).