Waste plastic can be converted into rock for decorative and utilitarian applications. A combination of sand and waste plastic is added into a tumbling chamber, and the tumbling chamber is rotated. The combination of sand and waste plastic is heated while rotating the tumbling chamber to form conglomerates. When a desired size of the conglomerates is achieved, the heating is stopped. Dry cement is then added to the tumbling chamber while continuing to rotate the tumbling chamber.