I believe that the use and popularity of coral beads supplanted an earlier use of carnelian beads—namely the pema raka beads that still circulate (and have been replicated in recent years by the Chinese). Consequently, I would not see carnelian as a substitute for coral, but rather it was the reverse of this. It is certainly also possible that one material might be more popular or preferred in one region or group of people over the other material. Do we know which Tibetans continue to wear the greater numbers of pema raka beads?

The wearing of both carnelian and coral provide the opportunity to have the color red in ornaments—and thus their popularity. Everywhere, red is a significant color in symbolism, and a popular color for its beauty.

Jamey