Haüy, René-Just (1743–1822)

French mineralogist, the founder of modern crystallography. He regarded crystals as geometrically structured assemblages of units (integrant molecules), and developed a classification system on this basis.

Haüy was born in Oise département. He trained as a priest, then became professor of mineralogy in Paris in 1802. During the Revolutionary era, he was protected from anticlerical attacks by Napoleon's patronage.

Haüy demonstrated in 1784 that the faces of a calcite crystal could be regarded in terms of the standard stacking of cleavage rhombs, provided that the rhombs were assumed to be so small that the face looked smooth. Similar principles would lead to other crystal shapes being built up from suitable simple structural units. He proposed six primary forms: parallelepiped, rhombic dodecahedron, hexagonal dipyramid, right hexagonal prism, octahedron, and tetrahedron.

His two major works are Traité de minéralogie/Treatise of Mineralogy (1801) and Treatise of Crystallography (1822).