Such spheres could have been formed in the air, a combination of dust and water fused in early Martian thunderstorm-like conditions, possibly engendered by meteor strikes in the early Martian "seas", or the product of waterspouts in combination with a very dry, dusty and thin atmosphere formed as Martian twisters intersect the dying, warm and very salty Martian seas. Perhaps these blueberries periodically spewed out of a Martian weather-feature as a product of such Martian conditions.
Hail and ice storms on earth sometimes form binary and triplets ice balls, if conditions are right.
The Martian "Blueberries" could have been formed as a mixture of dust and water coalesced in such a storm, and were "air dried" in much the same way as water is frozen in thunderstorms on earth.
Martian meteorologists should consider this angle as a possible cause of the blueberries, as a product of the conditions during various stages in the transformation of the Martian atmosphere over the eons.
Just a thought.