Lava rock can be purchased at most hardware and home improvement stores. Stores such as Walmart and Lowe's carry lava rock for landscaping. Many pet stores such as Petco also carry lava rock for use in fish aquariums and tanks.
According to The Home Depot, lava rock is not only used for decorative purposes, but can also help prevent erosion and retain soil moisture. Many people use lava rock because it does not fade like mulch. Lava rock is used in aquariums for decorative purposes and also because it helps beneficial bacteria grow in the aquarium, notes Grand Valley Aquarium Club.