The title 6
Apart from all those myths and magical properties, the gemstone has been around since classical literature.
Pliny the Elder called precious opal opallus or "precious stone". …
In Greek mythology, opal was formed from the tears of joy that Zeus wept after defeating the Titans. In Indian lore opal was formed when the Goddess of Rainbows was turned to stone whilst fleeing the romantic advances of the other gods. In the Arabic world it was believed that opals fell from the skies in lightning flashes which gave them their fire. …
With all these different symbolic attributions of opal it's perhaps not surprising that Shakespeare used it as a symbol of unpredictability and inconstancy.
— www.wyrdology.com
Clown: "Now, the melancholy god protect thee; and the tailor make thy doublet of changeable taffeta, for thy mind is a very opal."
— William Shakespeare, Twelfth Night
Shakespeare was among Syd's favourite reading material, and the Shakespearean character, the "Clown", fits Syd's "character" very well:
Feste, the "Clown", also known as The Fool, earns his living by making pointed jokes, singing old songs, being generally witty, and offering good advice cloaked under a layer of foolishness. In spite of being a professional fool, Feste often seems the wisest character in the play.
— en.wikipedia.org
Mendham, Trevor. Wyrdology. Web. http://www.wyrdology.com/stones/natural/opal.html
Shakespeare, William. Twelfth Night. 1602. Play. http://shakespeare.mit.edu/twelfth_night/full.html
Wikipedia contributors. "Twelfth Night." Web. http://en.wikipedia.org/wiki/Twelfth_night