There are various kinds of clay masks, some whose purpose is unknown.
1 (p. 182):
There is no hole for a string in this clay mask. It has the hollows of the eyes, where semiprecious stones seem to have been set. There are different opinions as to whether this is a mask and what its purpose and use were.
2 (p. 183):
Excavated from a location beside a grave. With durable holes for strings, it is speculated that this clay mask had been tied to the wooden grave-post.
The unearthed grave pit may have belonged to the owner of the clay mask.