And that is one reason why one offsets all seams in wood working and use long sticks for support.
Has it been determined why the marble separated or sagged?
Since most seams are bonded with epoxy, I would expect some epoxy with same shade of marble dust would be used to fill the gap.
More importantly would be getting the proper support under the counter top and making sure the support pieces span more than one base cabinet edge on either side of all seams or getting the pieces to but to each other. It might even need a steel or laminated support to carry the weight of the counter top. That is a rather long span for such a heavy counter top.
Has it been determined why the marble separated or sagged?
Since most seams are bonded with epoxy, I would expect some epoxy with same shade of marble dust would be used to fill the gap.
More importantly would be getting the proper support under the counter top and making sure the support pieces span more than one base cabinet edge on either side of all seams or getting the pieces to but to each other. It might even need a steel or laminated support to carry the weight of the counter top. That is a rather long span for such a heavy counter top.