BULLETIN FOR THE HISTORY OF CHEMISTRY
Volume 51, 2026
Jewess, Michael, “René-Just Haüy (1743-1822): Early Difficulties with Chemistry, Some Successes With Geometry, and an Unresolved Tension,” Bull. Hist. Chem., 2026, 51, 144-156.
https://doi.org/10.70359/bhc2026v051p144
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Abstract/Description: Commonly, Essai d'une théorie sur la structure des crystaux of 1784 by René-Just Haüy (1743-1822) is regarded as a foundational work of crystallography. This article studies its archetypal example, "spath fluor phosphorique," so as to illuminate two key insights provided by the Essai: (a) how to correlate by means of elementary geometry and trigonometry interfacial angle measurements made on crystals, including after cleavage; and (b) how likewise to relate the different crystal "habits" (modern term) of the same material. Both insights remain recognizable in modern crystallography, even after the development of X-ray diffraction of crystals in the twentieth century. "Spath fluor phosphorique" was confusingly named from the point of view both of a contemporary reader and of a modern one, but we show that it can only have been the mineral today called fluorite, CaF2, and explain the error as reflecting Haüy's lack of appreciation in 1784 of chemistry (then prevailingly phlogistic). This leads us to consider Haüy's subsequent increasing use of chemical results, culminating in the second, at least partly posthumous, edition of his five-volume Traité de minéralogie of 1822-1823. This used contemporary (non-phlogistic) chemistry as a primary classification tool, and included full third-party chemical analyses as well as interfacial angles, and was a valuable compilation of empirical information.