Hello Marin and welcome to the Community.
To dress up your fireplace you have many options. You could special order a piece of marble or granite. You could also install a slate, marble, ceramic or porcelain tile. I suggest you visit your local Home Depot and see the great variety of options both in the store and ONLINE.
For example, here is a natural stone Empress Green polished marble floor tile.
Alternatively, a Frontier Brown marble floor tile.
On the other hand, perhaps a Crag Aztec Multi Sunset Slate Mosaic tile.
Let your imagination go wild.
Thank you for your shopping at the Home Depot.
Charlotte.