Stone inkwell in the shape of a cartouche.
The ancient Egyptian scribe used black and red ink which would have been placed in a palette (inkwell). By the Third Intermediate Period cartouche shaped palettes such as this were made (see Friedman ed. 1998, 224). Often, however they are made of faience whereas this example is stone.
The cartouche is a protective symbol, usually used to contain the names of the king. Perhaps they were put around such inkwells to protect the work of the scribe, whose writings could have magical affect. Palettes too often have protective symbols such as the shen or cartouche, for example EC2018.
Friedman, F.D. (ed.) 1998 Gifts of the Nile. Ancient Egyptian Faience. London: Thames and Hudson