Rene-Just Hauy. Illustration of Rene Just Hauy (1743-1822), French mineralogist and the founder of crystallography. Hauy successfully trained as a priest but grew interested in crystallography in 1781. He had noticed that the fragments of a broken calcite crystal clove along straight lines that met at constant angles. In 1784 he showed that crystals were built up of tiny units; the shape of the crystal being determined by the shape of the units. Hauy helped Lavoisier to determine the density of water. In 1802 Hauy became a professor of mineralogy at the Museum of Natural History in Paris and wrote a crystallography book at Napoleon Bonaparte's specific request.