Rasmussen 20" Dark Gray Alterna Ventless FireStones Single Sided - AFS20-DG offers a bold and elegant look for ventless fireplaces. Crafted with durable ceramic-bonded refractory material, these dark gray firestones withstand high temperatures, providing long-lasting resilience without cracking. Perfect for concealing unsightly burners, they bring a modern, natural element to your space. Exclusively compatible with Rasmussen Alterna Vent-Free FireStones Burners (sold separately).