Sebastapol Chanuhacha collection, Bangkok, Thailand
Sebastapol is a self-described rock hound and writes: "I bought this "Rock of Skull" (so-called by the former collector, because of its actual-human-skull size and three- hole characteristic) from 70-year-old American Archaeological Professor who has kept it in his collection for over 40 years. This masterpiece of nature, he said, was collected somewhere near the bank of river around Niagara Fall by the local Indians long time ago. So, I believe, this rock has particular meaning to the Indians."
To me, it looks like a possible prehistoric serendipitous find which was chipped and trimmed to realize a more idealized face mask. Found objects like this deserve a close look to determine if they have been modified in the past. This piece seems a good candidate for an example of a "one eye open, other eye shut or missing" mask sculpture in the Lower-to-middle Paleolithic European motif, with distortion to the left side of the face as is seen in most other examples.
If the original archaeologist who collected this piece was aware of the common utilization of found natural forms as starting forms for art, and that this mask fits an already known and described motif, then he might have been able to contribute some more information about the context of this object or subject it to full petrology assessment of artificiality.