How can I repair a leaking crack in a Terrazzo stone bathtub?
I'm not an expert in this material, but here's my first inclination.

Turn the tub over in a good workspace.
Using a rotary tool (Dremel) or similar, channel out the outside of the crack to a depth of at least 1/4&quot; (6mm). Keep this channel just the width of a carving bit--say 1/8&quot; (3mm). Channel the entire length of the crack to a uniform depth, and taper out the groove just beyond the end of the crack.
Thoroughly clean out the channel with compressed air, alcohol, or soapy water (rinse well in the case of the latter). Allow it to dry thoroughly.
Fill the channel with a quality two-part epoxy. Work from one end and use masking tape to cover the channel as you work, containing the epoxy while it cures.
After curing, carefully sand the repair smooth with medium and fine-grit sandpaper, following any manufacturer instructions for such surface maintenance.
Reinstall the tub and test thoroughly.