silicates
Topaz
Al2SiO4F2
- Also known as
- imperial topazprecious topaz
- Crystal system
- orthorhombic
- Hardness
- 8 on the Mohs scale
- Lustre
- vitreous
- Colour
- Colourless, blue, yellow, brown, pink, rarely red
- Where it forms
- In granite pegmatites and in cavities in rhyolite, from fluorine-rich vapours in the last stages of cooling.
- Chiefly from
- Minas Gerais, BrazilNigeriaPakistanUkraineUtah, United States
Why it is that colour
Colour centres from irradiation and from trace chromium. Nearly all blue topaz on the market is colourless material that has been irradiated and then heated; natural blue is pale and uncommon.
Safety
Safe to handle. Irradiated blue topaz must be held after treatment until residual radioactivity decays, and in the United States and several other countries this is regulated and the material is tested before release. Properly handled it is safe; the regulation exists because the process genuinely activates the stone.
Where it comes from
Brazil dominates. Ouro Preto in Minas Gerais is the source of imperial topaz, the pink-orange material that is the only genuinely rare and expensive kind. Blue topaz is cheap because the raw material is abundant and the treatment is industrial.
Historical use
Perfect basal cleavage makes it difficult to cut and easy to break, which is why large topaz has always been more common in museums than in rings. The Braganza, a 1,680-carat stone in the Portuguese crown, was long believed to be a diamond and is topaz.
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
The classical name topazios referred to an island in the Red Sea and almost certainly to peridot rather than to topaz, so ancient references are unreliable. Medieval lapidaries treat topaz as a stone against melancholy. Modern colour-specific meanings are recent.
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
Blue topaz is worth understanding because it is one of the few treatments with an actual regulatory regime attached. Colourless topaz is bombarded in a reactor or an electron accelerator, which creates the colour centres that make it blue — and, depending on the method, makes the stone transiently radioactive. It is then stored, sometimes for months, until activity falls below limits, and in several jurisdictions it must be tested and certified before sale.
The finished stone is safe. But the reason a bright blue topaz costs almost nothing is that it began as one of the most common gem minerals on earth and spent time in a reactor, and it is striking how rarely either half of that is mentioned at the counter.
Identity checked against IMA-CNMNC master list, June 2025.