Try these folks for some help.

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Tim and LT, I found this BBS specifically geared towards Stone and Tile Restoration,
check out Stone Industry BBS. Read through some of their
posts for help and/or post your question. I noticed one post Granite Oil Stain where
the person had an olive oil stain on their granite top which would be similar to
your butter dish issue. Anyway, hope this helps!
Wick