large format tile? interesting.

Do you have room for a pencil tile to finish it off? What are the mitres finished with?

is it finished at the wall?

I would paint the indent black so your TV cords don't show against the white background.

you don't need any decor on the mantel.

A 1/2" white ceramic bullnose or pencil tile as suggested above..

A big gloppy white 1/4 round at the base. Yuck

I'd fill the gap with a seam filler that matches the floor tile.

Select a product that can be washed and will match the floor.

Second on Beverly's suggestion. This will provide a much better transition between fireplace tile and floor than a trim piece.

Thanks for somee great ideas!!!