There are plenty of things in Star Wars that can stop a saber strike. However, a saber can melt through most materials providing there's long enough contact between the blade and said object.

Example: neuranium, a metallic substance used to shield from radiation (essentially the sw version lead). James Luceno elaborates in Star Wars: Revenge of the Sith The Visual Dictionary, stating a millimeter can stop radiation, making it around 100 times more dense than lead.

Sidious' lightsaber was hidden deep within a cavity in the neuranium of a statue. The neuranium core of the statue was even able to resist a lightsaber blade activated inside it for several seconds. In these seconds, the neuranium glowed magenta to blood red to crimson before Palpatine's scarlet saber shot out of its core.

However, virtuous of being one of the densest materials in SW, does not make it stronger than Vibranium. Which has a multitude of feats showcasing it's indestructibility.