Our Volcanic Glass Ecoscape stone is not only an artistic choice for the home aquarium, but also a safe choice for both fish and plants. Volcanic glass is formed when lava from a Volcano cools too rapidly to form crystalline structures, giving it a glass silky appearance. Volcanic Glass is inert and will not alter pH or hardness. It comes in a variety of shapes and sizes handpicked by the Ecoscape team to give your aquarium a unique look.