Three Kings Charcoal disks brand of foil-wrapped roll of 10 charcoal disks for burning herbs, resins or loose incense.
I like to place an inch of sand in the bottom of my burning bowl, and then place the charcoal on top of that. The charcoal will get very hot, and sand will absorb the heat, protecting your vessel.
This is the brand used in cathedrals in Europe, and is very reliable.
Made from hardwoods.
No nasty chemical scent.