Is that limestone?  Looks like glue or mastic coming through perhaps. I would twst a few tiles with a good color enhancer. May not remove the issue but may make it easier to live with.
B

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> On Jun 2, 2017, at 9:36 PM, Stephen Webb <stephen@newlifemarblerestoration.com> wrote:
>
> Greetings All, Can anyone explain what we are seeing and what caused it?  I don't think its practically restorable .
>
> thanks
>
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