Related Clues

• Collectible, maybe
• Blue moon, e.g.
• Hen's tooth, e.g.
• Hole-in-one, e.g.
• Hole in one, e.g.
• One for the books
• It doesn't happen often
• It hardly ever happens
• Something unusual
• Uncommon occurrence
• Seldom-seen thing
• Diamond value factor
• Curio
• Curio
• Uncommon item
• Collector's item
• One-in-a-million thing
• Blue moon, for instance
• Albino, for one
• Uncommon thing