The answer is: An onyx

Exo 28:9 - to be part of the priestly ephod

The use of onyx for engraving the names of the twelve tribes of Israel is deeply symbolic. Onyx is a specially layered stone known for its captivating shine, often representing strength and protection in many ancient cultures. In Exodus 28:9, it’s connected to the priestly, declaring that the high priest, wearing the ephod, would bear these names before God, interceding for the tribes. It shows the high priest’s role as a mediator advocating for the people—quite the responsibility!

Now, let’s not overlook the symbolism behind having each tribe represented. Twelve, being a complete number (think of the twelve months, or hours on a clock), reinforces the unity of Israel. It suggests that every individual tribe has a voice that matters in God's eyes.

Interestingly, the use of gemstones in priestly attire isn't unique to this occasion. The Book of Revelation also illustrates a recreation of divine elements with jewels, referring to the New Jerusalem adorned with precious stones. There’s a connection to history here; what was once a physical representation in the tabernacle evolves into a spiritual imagery of celestial promise.

Also, how cool is it that ancient artisans carved onyx meticulously! Gem-grinding and stone artistry was a highly respected craft back then. These details pull us into the richness of biblical culture, reminding us that the faithful ceremonies extended far beyond mere ritual to encompass deep ties and interconnectedness within the community.