I’ve read that Opals were first associated with bad luck due to some
timing with the “black death” plaque but I can’t remember the full
story. There is also this:
"In the nineteenth century, opal was considered unlucky due to the
plot of a popular Sir Walter Scott novel of the time. The heroine of
the novel has her life force caught in the beautiful opal she wears
in her hair and she dies when the fire in the opal is extinguished."
from the International Colored Gemstone Association.