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The liquid soap probably has oil in it so your hands don't get dry when you use it. That oil needs to be broken down in the stone. Of course, you should try to pull it out first with a poultice of baking soda and water. Your cost will be about 1/10th of one cent to try that.
If several attempts at that doesn't remove it all, which it probably won't, you'll need to break it down with something. I'd recommend tiny tests of several things in inconspicuous spots, if possible. First, try bleach, regular strength. Second, you might try some acetone.
After that, report your results and we may get more creative.
And might I humbly suggest you try resealing with a permanent, invisible sealer?