silicates
Dumortierite
AlAl6BSi3O18
- Also known as
- blue denim stonedumortierite quartz
- Crystal system
- orthorhombic
- Hardness
- 7–8.5 on the Mohs scale
- Lustre
- vitreous
- Colour
- Deep blue to violet, sometimes pink or brown
- Where it forms
- In aluminium-rich metamorphic rocks and in some pegmatites.
- Chiefly from
- MadagascarBrazilNevada, United StatesFrance
Why it is that colour
Iron and titanium. It is one of the very few strongly blue aluminium borosilicates.
Safety
Safe to handle.
Where it comes from
Common, and mostly sold as dumortierite quartz — quartz containing dense blue dumortierite fibres, which is harder and more durable than the massive material.
Historical use
Used industrially in high-grade porcelain and in refractories, because it converts to mullite on firing.
Recorded as history and attributed where possible. That a stone was used for something establishes that people used it, not that it worked.
What is attributed to it, and since when
Described in 1881 and named after the French palaeontologist Eugène Dumortier. No traditional attribution.
Described, not endorsed. Dating a claim is not the same as assessing it — but an association that first appears in a book published in 1985 is not an ancient inheritance, whatever the label says. A sincere account of feeling better is compatible with the stone doing nothing — see the placebo effect.
Sold as this, but not
Worth knowing
Dumortierite closes the circle back to rose quartz. The fibrous inclusions that make rose quartz pink are a dumortierite-related borosilicate, dispersed through the quartz at a scale too fine to see. The same mineral family, in visible quantity, makes a deep blue stone; in microscopic quantity, it makes the palest pink one in the shop.
That is a nice illustration of how much of mineral colour is about quantity and scale rather than identity.
Identity checked against IMA-CNMNC master list, June 2025.