The title
The main issue about the title is whether it should have been "Opal", or actually "Opel". Though Syd presented the title to Malcolm Jones, who wrote it in his book aware of its correct English spelling, the common theory is that the title was misspelled by whoever wrote it on the recording sheet.
Besides the gemstone and the car manufacturer, the most common use of both words is as a female name. Both names are from Indian (Asian) origin, so an Indian girl with a totem on her necklace, standing on an island, is already a suggestive theme. After all Syd presented "Opel" as new material together with "Swan Lee" which was about a Native American girl, and later he sang about a girl named Pearl in "Dolly Rocker". An Asian beauty like Syd's girlfriend Iggy might come to mind,* but the images Syd describes in "Opel" don't seem to be written for a girl, nor do they recall a girl any more than a "pebble stood alone" recalls a gemstone. In any case, it's interesting to know more about both the names, leaving aside the gemstone:
- "Opal" is a fairly popular name in America, birthplace of the charismatic, mysterious writer Opal Whiteley, who lived in an asylum not far from Cambridge and is surely the "Opal" who is the most likely to have been inspirational for Syd.
- "Opel" as a first name doesn't lead to any famous person as "Opal" does in a normal search. Though there was a talented soul-ska singer-songwriter called Jackie Opel, in this case the Hebrew origin of the word "Opel" fits the song better than the Indian origin.
* Later known as "Iggy the Eskimo", she lived in Syd's house for a couple of weeks and wasn't officially his girlfriend. Probably, according to his former girlfriend Jenny Spires, all his songs were already written.