Wooden model illustrating Haüy's laws of decrement
France, early 19th century
The model (height 7 cm) illustrates a complex differential decrement of cubic "molecules" on the edges AND on the vertices. It results from a combination of Haüy's laws giving the octahedron starting from the cube combined with that giving the pyritohedron and exemplifies crystal forms of pyrite ("sulfure de fer icosaèdre" of Haüy).
Haüy R.J. Annales de Chimie, 17, 225-319 (1793)