try using a standard marble cleaner from your local home center. If that doesn't work, you might want to contact a professional. Many cleaning methods can etch marble which damages the finish.
Every time I clean my mirrors, they end up having tons of streaks and almost look worse than before I started. What could I use to clean them that won't leave streaks...
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What kind of stains? Was it sealed after installation?
try using a standard marble cleaner from your local home center. If that doesn't work, you might want to contact a professional. Many cleaning methods can etch marble which damages the finish.