This lightweight gemstone is sometimes confused for sodalite or lapis lazuli. Lapis is considerably heavier, much rarer and more expensive. Sodalite usually has more of a royal blue colour and stones take on a deeper polish.
On Mohs scale of mineral hardness which is a scale that measures the scratch resistance of one mineral against another, dumortierite grades 8. Diamond which is the hardest mineral on the scale grades 10.