This is an old Chinese Instone - which is a stone mortar for the grinding and containment of ink. Inkstones were made from stone, clay, bronze, iron and also porcelain. This one appears and feels to be river stone. This inkstone measures approximately 6 inches long and 4 1/2 inches wide. It is a two-piece design and appears to have been used at one time for making ink. The top is highly ornate and adorned with dragons.
This appears to be Pinyin She inkstone made from stone similar to slate or Duan stone from a mine, which was first used in the Tang Dynasty. It could also be Chengni style inkstone - also originating in the Tang dynasty as a type of ceramic-manufactured inkstone.