Gluing Acrylic to Glass
Oceanic uses GE Contractors Silicone SCS 1200 to glue the acrylic corner boxes into glass tanks. U.S. Plastic* sells SCS 1200 in translucent and assorted colors in caulking gun sized tubes. The key to a good bond is for both surfaces to be completely clean, as even one fingerprint will cause the Silicone not to adhere well to it, creating a poor bond. Always allow 48 hours for it to dry and another 7 days to cure completely.
should work for slate