I was doing some recreational programming recently, all related to spam filtering.
Tino requested that I take in a number of texts (meaning text files of actual books, 12 of them) and figure out which letter pairs never occur in natural language. I did that, and while checking my work, I found "yx" from the word "sardonyx" (meaning it does occur). I figured this must be a user name from one of the Neal Stephenson books since it sounds like a superhero who's special power is being derisive. I grepped all the books, and the source surprised me. It was the King James bible, from Revelations:
21:19 The foundations of the city's wall were adorned with all kinds of precious stones. The first foundation was jasper; the second, sapphire; the third, chalcedony; the fourth, emerald;
21:20 the fifth, sardonyx; the sixth, sardius; the seventh, chrysolite; the eighth, beryl; the ninth, topaz; the tenth, chrysoprasus; the eleventh, jacinth; and the twelfth, amethyst.
21:21 The twelve gates were twelve pearls. Each one of the gates was made of one pearl. The street of the city was pure gold, like transparent glass.
Apparently, it's some sort of gemstone. You learn something new everyday, I suppose.