Exodus 39 describes a set of wonderful stones, each placed in one of four rows in the High Priest's breastplate:
And they set in it four rows of stones: the first row was a sardius, a topaz, and a carbuncle: this was the first row. And the second row, an emerald, a sapphire, and a diamond. And the third row, a ligure, an agate, and an amethyst. And the fourth row, a beryl, an onyx, and a jasper: they were inclosed in ouches of gold in their inclosings. And the stones were according to the names of the children of Israel, twelve, according to their names, like the engravings of a signet, every one with his name, according to the twelve tribes.
Aldous Huxely, in his essay Heaven and Hell, asks what it is about precious stones that make them precious? He suggests that they are actually the closest physical objects that exist in this world that resemble the world found in the human mind's remotest regions, what he calls the Other World.
Men have spent enourmous amounts of time, energy and money on the finding, mining and cutting of coloured pebbles. Why? The utilitarian can offer no explanation for such fantastic behaviour. But as soon as we take into account the facts of visonary experience, everything becomes clear. In vision, men perceive a profusion of what Ezekiel calls "stones of fire", of what Weir Mitchell describes as "transparent fruit". The things are self luminous, exhibit a preternatural brilliance of color and posses preternatural significance. The material objects which most nearly resemble these sources of visionary illumination are gem stones.