Please show the entire space from all four walls. Here's why:

You might just be asking about a tiny feature in your space. Design people need to evaluate the whole space to see where an indivdual feature can or can't fit in terms of size, color, shape, finish, style. Everything that comes into a room, or is already there and staying, needs to relate to everything else. TAKE PHOTOS FROM ALL FOUR WALLS, INCLUDING ADJOINING SPACES.

a high adhesive primer first... like KILZ

It might be a very good casting job, but your fireplace surround looks like an actual polished Travertine surround to me.

• You can paint over stone. IMO it won't look very good but it can be done.
• You could see if a stone guy could come in with a wet grinder and change the finish on the stone from polished to honed, but it might ruin your floor.
• You might be able to spray a clear matte finish over the stone to kill the shine.

Here's a travertine fireplace surround with iron finishes in lamp, candle holders, natural basket of chunky logs. These rustic finishes and elements connect to the surround yet give off a casual vibe along with wood floors, chaise longue, nubby rug if that's the direction you're going in. No idea what you're trying to achieve by de-glossing the stone.

Now that I see the comments, it must be travertine. I know the builder worked with a local tile/stone company and there is a lot of stone throughout the house.

I do not like how formal it is and it dates the house to when it was built, which was early 2000's. The shine and color are not my favorite.

Again, if you show us the entire space, many people on Houzz can help you figure out a way to create a less formal vibe for your living room with art, rugs, lighting that will minimize the formality you don't like. As for the color, it harmonizes very well with your floors, so probably everything you choose should work with the floors as well.

The surround leans to Mediterranean style, but frankly, the size and scale of the surround it grossly proportioned and it doesn't fit on the small wall. No painting or de-glossing is going to fix that problem.

Something more like this would be a better fit.

I wonder if you could get someone to take off the mantle and the mantle sides and see what you have to work with underneath. It looks like those parts of the surround were set against the wall and not built in.

Even if you tone down the gloss, the style will still look very formal.

I just added a photo from the real estate listing. I did not hang a TV over it, I have a piece of artwork there instead. Regardless, it actually does fit in the room because the house is quite large with 10' ceilings and lots of open space. I was just wondering about changing the finish but I will likely enjoy it as it is and consider replacing in the future.

I have not tried this product, but it might be the solution to turning your glossy travertine into a matt finish. You could also try matt finish clear spray paint.

https://www.amazon.com/FILA-54000012-Matte-Finish-Protective/dp/B00EDYME30?ref_=ast_sto_dp

What is the space behind the fireplace? The opening is making me curious.

Waiting till you have an alternate plan (removal and a new mantle) sounds like a good idea.

Here's a pretty formal fireplace, but the art work above it and TV to the side on a modern console work very well to make the entire wall visually interesting, not just the fireplace.

Soul, Grit, and Emotion · More Info

Notice the various elements in the room that add modern touches to a room with traditonal fireplace: pipe bookshelves; art work; roman shades; textured patterned rug. All these elements balance out the traditional fireplace.

Park Slope Brownstone · More Info

Shelving to right of this fireplace adds balance and liveliness to the space. There's a lot you can do to the space on the right of your fireplace to get this effect.

The Bryant Back Bay · More Info

RESIDENTIAL PROJECTS WOOD MODERN LOOKS ARD · More Info

I would bet that it is just clad in 2cm Travertine over a wood frame. Not a difficult project to remove it and have it redesigned with a different stone/tile and wood mantle.

Maybe you can have it honed so it’s not so shiny?