Abstract: Vitreous, algae growing materials, release stably ferrous ions, over long periods of time. The duration of ion release can be controlled as desired by adjusting the particle size of the materials. The vitreous, algae growing, materials can be converted into porous forms or fabricated into at least parts of structures. The vitreous, algae growing, materials consist essentially of 15 to 50 weight percent SiO2, 1 to 35 weight percent either or both of Na2O and K2O, 30 to 70 weight percent B2O3, and 1 to 40 weight prercent of either or both of FeO and Fe2O3. Increasing the content of boron facilitates the release of ferrous ions from the vitreous, algae growing, materials.

Abstract: A process for the formation of an artificial seaweed bed comprises depositing a structure as an artificial fish reef in the sea. According to the present invention, the structure is made of a glassy material having a specific composition, or a surface of the structure is covered with the specific glassy material. The glassy material contains silicon in an amount of 30 to 70 wt. % in terms of SiO.sub.2. The glassy material further contains sodium and/or potassium in an amount of 10 to 50 wt. % in terms of Na.sub.2 O and/or K.sub.2 O. The glassy material furthermore contains iron in an amount of 5 to 50 wt. % in terms of Fe.sub.2 O.sub.3. All or a part of the iron is present in a ferrous state. The glassy material contains the ferrous iron in an amount of not less than 1 wt. %.