Based on the information in the description above at the linked image page, you could measure the small hole, in micrometers. You would be required to have the figure for a MAHLI turret position to obtain the measure.
The image below gives a view of nearby rocks bearing a large distributed portion of small spheroids.
The small pebbles on the rover were about 1-3 millimeters, some larger, some smaller. They were irregular in shape.
Why would the occasional hole be present in layered material? Why a round shape to the hole? Why a single hole?Are you considering answers for this?
Would a single spheroid be a sufficient reason for the hole like your topic image shows?
Do you believe the layering is caused by chemistry or deposition in this area?