From the edges it looks like it could be some sort of limestone that maybe has a sealant on the top that turned it a bit yellow? You might be able to get a stone fabricator to pop it off and hone the top so the finish is matte like the edges, not shiny. But that may end up being just about as expensive as replacing it altogether. Get some quotes so you can compare the difference.

Yeah, that’s just limestone ledger. Ok, I know I’ve posted about how much I love my soapstone countertops, but I swear this isn’t just another gratuitous plug. Soapstone will give you a much nicer color, but the best part is that it absorbs and retains heat for a really long time. It is an amazing fireplace product! Belgian Bluestone will also be nice, though possibly harder to find and a bit pricier.

Here are a couple of soapstone, and one bluestone. Domestic bluestone is less expensive and either can be honed or chiseled face for a more rustic finish. Stone fabricators that handle countertops can help you best.