Growstones: Sustainable Perlite Alternative from Recycled Glass (Product Overview)

In a quest to find as many options for gardening as possible, I've come upon Growstones. Growstones are a replacement for perlite. Perlite is a mined volcanic rock which is super heated and then expanded by 10 to 20 times the original volume. In horticulture, perlite is very commonly used, especially in soilless potting mixes. But is perlite "sustainable"? Is the use of perlite good for the environment? Many gardeners have asked that question. Some have decided they want to avoid perlite. Be