The hearth is approximately 16'x18"x4". It is concrete and it's supported with custom brackets

I love the look and I want something similar with the fireplace I'm having installed! Forgive my ignorance, but is the concrete poured into a mold to achieve it's rectangular shape? How do you achieve the shinier, black finish? I appreciate any guidance you can give!

This was cast off site in my shop. A custom form is made for every project. After the concrete has hardened it is polished and sealed. The whole process from start to finish takes about 2 weeks. The color is achieved using pigment which is mixed into the concrete.

Thank you so much for the info! I've looked at a limestone sill to use as the hearth, but it's not dark enough. I also looked at honed black granite, but two pieces of granite would have to be laminated to make it thick enough...still only 2 1/2". I like your 4" polished concrete hearth much better! Thanks again!

No problem. If you need help finding somebody locally let me know. Depending on where you live I may be able to recommend someone.