Law of rational indices and integrant molecule (Haüy)
Ley de los índices racionales y molécula integrante (Haüy)
- Date
- 1784 · confidence high
- Place
- Paris, France
- Credited to
- René-Just Haüy
- Field
- Cosmos & Earth
What was discovered
Haüy explained that each crystal is built by stacking tiny identical units obtained through cleavage (the 'integrant molecule'), so that the crystal's faces relate to the lattice by simple integers. He founded geometric crystallography.
The anecdote of the dropped calcite (1781) is probably a later legend. The law of rational intercepts was formulated rigorously later (Weiss 1809, Miller 1839). Romé de l'Isle (1783) had already established constancy of angles.
What it led to
- geometric crystallography and crystal systems
- classification of minerals by form and composition
- a step toward Bravais lattices