The fifth foundational stone in New Jerusalem (Revelation 21:20), which is like the onyx, is called sardonux in the Greek (Strong's #G4557). Strong's states the word refers to the nail of a finger (probably due to its flesh tone color) and both it and Thayer's lexicon translates the word as "sardonyx." Thayer's states the sardonyx was a stone containing red and white colors.
Onyx and Sardonyx stones are a variety of agates, which themselves are a variety of chalcedony. Onyx gemstones possess black and white bands that tend to be parallel with one another. A Sardonyx (the prefix "sard" means "red") has parallel red or reddish bands instead of black.
The Bible states the onyx stones were found in the "whole land of Havilah" (Genesis 2:11). This gemstone is referred to at least eleven times in Scripture, more than any other precious stone. King David, after he officially made his son Solomon the new human ruler over Israel, set his heart to collecting and preparing materials for building Jerusalem's temple. One of the special materials he collected for the temple his son would build was onyx gemstones.
And David the king said to all the congregation, "Solomon my son, whom alone God has chosen, is young and tender . . . Now I have prepared with all my might for the house of my God the gold for things of gold, and the silver for things of silver, and the bronze for things of bronze, the iron for things of iron, and wood for things of wood, onyx stones . . . in abundance (1Chronicles 29:1 - 2, HBFV)
Anciently, according to the Catholic Encyclopedia, the onyx stone was mined in Egypt, Arabia and India. It has a long history of being used in jewelry and in pottery items such as bowls.
(First Century A.D.)
An onyx stone worn around the neck was believed to cool the passions of love. This made it a popular gemstone to wear in India. One major side effect, however, of wearing the stone was that it supposedly encouraged discord and separation of couples (Curious Lore of Precious Stones, pages 98 - 99).