Is it okay to cut down a textured mold to fit a smaller kiln?

I'm wondering if anyone can tell me if I can use granite tiles as a glass dam for fusing. I have granite "samples" that vary in size from about 3" x 4" and 3" x 6". One side is polished. I was thinking that if I lined them with fiber paper and thin fire paper that I could use them as a dam. I don't want to ruin my kiln. I previously used them in my fireplace as a brace for the screen. I'm pretty sure they are dried out. Any ideas or help will be greatly appreciated. Thanks!