Walter, I remembered a passage from an article re: diamond drilling, and found the link. Also attached is a second short article with references to drilling ancient beads. There are probably better articles out there, but hopefully these will provide some background until others more knowledgable respond.

"More recently, we have uncovered preliminary evidence for the use of a drill utilizing diamond splinters as cutting points (Gwinnett and Gorelick 1986). These were used in ancient South Arabia, Iran, and Sri Lanka. It is known that diamonds were abundant in ancient India and that craftsmen learned to haft and use them for drilling. Indeed, the practice is still carried on in Cambay, India. The regular, concentrically grooved sidewall pattern of the parallel-sided perforation (Fig. 12) and a small, central conchoidal- fracture pattern at the leading edge of drilling (Fig. 13) are characteristic of this type of drill."

https://surface.syr.edu/cgi/viewcontent.cgi?article=1100&context=beads

"The actual drilling of the bead blank is one of the most difficult and critical steps in beadmaking, and the specific type of perforation used to make stone beads, whether by pecking or drilling, has turned out to be an informative detail of ancient lapidary that was never fully appreciated by earlier scholars."

https://www.harappa.com/sites/default/files/pdf/Kenoyer2003_Stone%20Beads%20and%20Pendant%20Making%20Techniques.pdf