Clay rock/clay ball/light expanded clay (LECA) is light weight natural product stable to varying pH and EC. Used as aggregrate for hydroponic, aerophonic and aquaponic. 
Lightweight, round to potato shape, natural product stable to varying pH and EC. Size 8 - 15 mm
Can be use at the bottom of pots for good drainage of water.
Less likely to break. Compact and last longer and can be reuse.
Improve aeration and root growth.  Does not hold much water hence less root rot.
Can be use in orchid potting mix, to cover the soil of potted plants to look attractive and to grow money plants hydroponically. Wash with water before use