That's because it isn't oak.
I started poking around this old bone yard where the original piece for the mantel came from (Actually it was in a dumpster nearby. Lifting it out was fun) I spoke to the owner. He told me his brother helped build a tall masted ship decades ago and he grabbed the cutoffs from the beams, put them in the boneyard, and just let them weather. He just kept them around thinking somebody might need them. I'm somebody. It took a whole lot of moving old aircraft parts to get to the ones that are worthwhile. They are HEAVY.
Here they are in the old truck. I called around, but nobody will mill stuff they didn't sell you. I called Byron, who is dropping everything tomorrow so he can help---I'm lugging them up to OC where he's got big tools and we'll see if we can cut them up.
I'm pretty sure they're teak.