Where does the ullage (empty space) around a diamond crystal embedded in kimberlyte come from?"?

Question

Kimberlyte is the diamond bearing ore mined in pipe formations.

Answer 1

Kimberlite is the transporting rock that brings up the diamonds
the blue ground as is called may be solid at the time of transporting to the surface diamond is harder causing wearing.
Some links Type in "The Nature Of Diamond"in browser.
Gems and Gemmology 1991 Spring Volume 27 . Pages 2 to 25
from Gemmological Institute of America.
Or Type in Your Gemmologist