They got into a fight
Oliver and Mark had a massive disagreement. When Oliver asked for the stone back, Mark refused. Oliver no longer had the authority to act in this manner. He calmed down a little as more people entered the business.
Where’s The Stone
Eventually, Oliver decided that he needed his rock back, and Mark appeared unexpectedly in the workshop. He couldn’t find his stone, but he was certain it was still around. Mark stayed close to Oliver once he got in, and the two continued to argue. Mark eventually succumbed to the pressure.