Also purple and white. From the French Bleu Jaune (blue yellow). Blue John is a rare, semiprecious mineral, it is a blue/purple and white/yellow banded variety of fluorite. Seldom found in jewellery because of its rarity.
Known as trystine or its trade namebolivianite, it's a variety of quartz. It is a mixture of amethyst and citrine. Ametrine is most typically faceted in a rectangular shape with a 50/50 pairing of amethyst and citrine.