We've just installed our new fireplace insert, which has about a 14" offset requirement for a mantel shelf. This would put it at over 57" on the top (assuming a 4" thick mantel), so we're thinking of putting in a non-flammable shelf instead.

I'm thinking of just getting a 4" x 6" x 6' beam and putting granite on the top and bottom. Two questions, which kind of wood would be best for the beam (would hickory work?), and is granite a good solution? I was looking at some concrete mantels - they're pretty heavy and expensive (150 lbs and $2,000 delivered), so I'm considering other options now.

Any ideas?

Thanks!