The name comes directly from the name of the gemstone. October is the birthstone for the Opal. The origins of the word itself are derived from the Sanskrit word upala meaning “jewel.” The name does not appear in the U.S top 1000, and the highest it ever ranked in American naming history was back in 1911, coming in at # 81.
The Opal was often seen as a source of bad luck in modern superstition, this was most likely due to a book published in 1820, entitled Anne of Geierstein by Walter Scott, the novel recounts the story of the Baroness of Arnheim who wears a magical opal talisman, when holy water is poured on the stone, the stone turns into its signature opaque white and the baroness dies. In the Middle Ages, the stone had far more auspicious connotations, it was believed that the stone brought great luck, since it sparkled several different colours, it was believed to hold the powers of every precious stone, making it a very powerful amulet.
The name is borne by Opal Whitely (1897-1992), a curious woman who wrote a diary in which she reveals her true origins as the scion of French royalty. The story is a famous part of American unsolved mysteries and she has had people debunking her as a fraud to admiring fans who support her claims known as Opalites.
With the rising popularity of the name Ruby, this might make an appealing alternative. There is the French form Opaline.