It is widely believed that Michaelangelo's favorite medium to work with was Carrara marble. The single gigantic piece of quarried marble had been more or less ruined a generation earlier by the efforts of the sculptor Agostino who had carved deeply into the block. It languished for 25 years exposed to the elements in a cathedral yard, the surface becoming rough with erosion.
It is said that the block had a single chiselled hole going into it roughly halfway up, that made carving a figure out of impossible. Michaelangelo rose to the heroic challenge, and created David by angling the youth's body in sort of an L-shape, with that chiselled divot touching somewhere on his torso.
Carrara marble is like most marbles, made from metamorphic sedimentary carbonate, usually limestone. David is made from calcium carbonate (CaCO3).
And so are antacids that you may typically ingest after too rich a meal in order to settle your stomach. Too much calcium carbonate has been reported to have dangerous effects (including writhing in pain, vomiting and altered mental state) but small amounts can be recommended for relief from gastric discomfort.
While marble dust may be dangerous for sculptors and artisans to inhale, actually ingesting small amounts of the dust from the labor of sculpting would do no harm, and could even have helped ease the queasy feeling Michaelangelo had while working for temperamental Popes.
(Apologies to Tums for use of their vintage advertisement, and even more to the ghost of Michaelangelo. Scuse, Maestro.)