To transfer the texture onto the polymer clay, drape a sheet of polymer clay around the stone and press firmly. When done, re-position the sheet of clay and repeat. Actually, it is better to have a few of those peach stones to avoid obvious repetition of the texture.
To prevent the clay from sticking to the surface of the peach stones, spray the polymer clay sheet with some water first. Other release agents could be used as well, such as mica powders or corn starch. I personally prefer water.
Look for more ideas for various texture tools in my Faux Metal Necklace Tutorial.