How do I clean marble that has a large lime. Buildup

Marble is limestone that has been compressed over a long period of time so chemicals will not be a good idea. Marble also erodes in weather which is why you seldom see it used in new tombstones. It would be extremely helpful if you would share what you have tried so we don't have to suggest that. It would also be helpful to know if this is at a cemetery or is a decor piece in your home and whether it is a polished surface or rough. On a rough surface I would try a wire brush in a rotary tool to remove efflorescence. On smooth surfaces sandpaper, working with increasingly fine grits until you are using a wet paper in the 1000s, then polishing with polishing compound to get the shine back.

Here are a couple of headstone specific sites, see what you think?

https://www.loveliveson.com/how-to-clean-granite-headstones/

http://www.gravestonepreservation.info/articles/cleaning-gravestones-monuments-stone-sculptures