Songhua stone is classified as an argillite, and is a member of the sedimentary rock family. It became highly valued during the late 17th century as a direct result of the Kangxi Emperor's fondness for the material. With its unique and attractive green striations and renowned ink-grinding quality the stone became a staple of the Palace carvers.

Agrellite is thought to boost the immune system. It is believed to combat infection and reduce swelling. It is also thought to help detox, and counter the side effects of chemotherapy.