http://www.opalsdownunder.com.au/articles/luck.htm
"The saddest opal saga is the oft-repeated misconception in the last of Sir Walter Scott's novels, Anne of Geierstein (1829), which irrevocably linked opal to misfortune. Having not read the third volume, the public jumped to the conclusion that the heroine has been bewitched, that her magic opal discolours when touched by holy water, and that she dies as a result. On carefully examining the texts, Si Frazier, writing in Lapidary Journal, found all three accusations false. The opal, which actually belonged to Anne's exotic grandmother, turns out to have turned pale as a warning to its owner against poisoning (which was the actual cause of her grandmother's death). Even so, this single work plunged opal prices to half in just one year and crippled the European opal market for decades.
George F. Kunz, author of "The Curious Lore of Precious Stones", says, "There can be little doubt that much of the modern superstition regarding the supposed unlucky quality of the opal owes its origin to a careless reading of Sir Walter Scott's novel, 'Anne of Geierstein'. The wonderful tale... contains nothing to indicate that Scott really meant to represent opal as unlucky."
In fact, in Roman times, the gem was carried as a good luck charm of talisman, as it was believed that the gem, like the rainbow, brought its owner good fortune. It was also referred to as the "Cupid Stone" because it suggested the clear complexion of the god of love.
Early races credited opal with magical qualities and traditionally, opal was said to aid its wearer in seeing limitless possibilities. It was believed to clarify by amplifying and mirroring feelings, buried emotions and desires. It was also thought to lessen inhibitions and promote spontaneity. The early Greeks believed the opal bestowed powers of foresight and prophecy upon its owner, while in Arabian folklore, it is said that the stone fell from heaven in flashes of lightning. To the Romans, it was considered to be a token of hope and purity.
In the 7th Century it was believed that opals possessed magical properties and centuries later Shakespeare was attributed with the description of opal as "that miracle and queen of gems". The Arabs believed that they fell from the sky, and the Oriental traditions referred to them as "the anchor of hope". Lucky opal - the stone of hope, the birthstone of October."