From the experts:
Opal is on the verge of a repolishing, following other jewel names like Ruby and Pearl. A Top 100 name during the first two decades of the twentieth century, the opalescent Opal has a good chance of coming back as another O-initial option.
The ancient Greeks believed that opals were formed from the tears of joy wept by Zeus when he defeated the titans, and that the opal bestowed prophetic powers; the Romans considered it a symbol of hope and good fortune. It was a favorite gem of Queen Victoria.
Opal Pelis is a character in Theodore Dreiser's seminal 1925 novel An American Tragedy.
And keeping with the O theme, Opal is the birthstone of October, making it an appropriate choice for a little girl born in that month.