René-Just Haüy

Educated in Paris and ordained a priest in 1770, Haüy's scientific destiny was triggered by an accident: dropping a specimen of calcareous spar (calcite) belonging to a friend, he observed that the fractured fragment broke along smooth rhomboid planes identical in angle to smaller crystals.

Haüy systematically cleaved crystals of diverse minerals, proving that every crystal species possesses a fundamental primary nucleus (unit cell) stacked in mathematical stepped layers. In his 1801 Traité de minéralogie, he formulated Haüy's Law of Rational Intercepts, founding mathematical crystallography. His brother Valentin Haüy invented books with raised print for the blind.