Dumortierite Gold Vermeil Bracelet I (8mm)The stone of the unshakable mind. It was named for the explorer who sought the worlds rarest minerals. Product Highlights: The Stone: Millions of years of history. Dumortierite is an aluminum borosilicate mineral, rare for its ability to produce such a deep, fibrous blue color naturally. It forms in aluminum rich metamorphic rocks, where its needle like crystal structure creates a dense, durable stone that is much harder than most other blue gems.