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Below are some stones I have in the order they appear, left to right: Grey La Lune (as opposed to purple), Special Stone and Pyrenees. Please also see their reverse sides appearing respectively...

May I ask why you thought it may have been a La Lune - is it from France? If so, it may be a Pyrenees stone, a coarser stone to use after a 1k, between 2-6k. Here is an example...