oxides
Smoky quartz
SiO2
- Also known as
- cairngormmorion
- Crystal system
- trigonal
- Hardness
- 7 on the Mohs scale
- Lustre
- vitreous
- Colour
- Pale grey-brown to near black
- Where it forms
- In granite pegmatites and alpine fissures, particularly where the host rock is rich in radioactive potassium, uranium or thorium.
- Chiefly from
- the Swiss and Austrian AlpsColorado, United StatesBrazilScotland
Why it is that colour
Natural radiation. Aluminium substitutes for silicon, and radiation from surrounding rock knocks an electron loose to create a colour centre. The stone is, in a literal sense, a record of how much radiation the ground it grew in has emitted.
Safety
Not radioactive itself, despite how it forms — the radiation did its work long ago and left no source behind. Safe to handle.
Where it comes from
Widely available from many sources. A large share of very dark, evenly coloured material on the market has been artificially irradiated to deepen it, which is stable and leaves no residual radioactivity but is rarely mentioned.
Historical use
The national stone of Scotland in practice if not in law, set into the hilts of dirks and into brooches, and named for the Cairngorm mountains where it was collected. Queen Victoria's enthusiasm for Highland style made it fashionable across Britain.
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 Scottish variety, cairngorm, has a documented traditional standing in Highland dress and jewellery, but as an ornamental and regional stone rather than a protective one. The modern association with grounding and with absorbing negative energy is New Age, from the 1970s and 80s.
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
The formation mechanism is the interesting part. A smoky quartz crystal is a natural dosimeter: the depth of colour records the radiation dose it absorbed while sitting in the ground, which is why the darkest specimens come from granites with the most uranium and thorium in them. Geologists have used the effect to estimate how long crystals have been in place.
Which produces a small irony worth noticing. The stone most often sold for clearing and protection is the one whose defining feature was produced by radioactive decay.
Identity checked against IMA-CNMNC master list, June 2025.