silicates
Labradorite
- Also known as
- spectroliteblack moonstone
- Crystal system
- triclinic
- Hardness
- 6–6.5 on the Mohs scale
- Lustre
- vitreous
- Colour
- Grey to dark grey, with blue, green and gold flashes
- Where it forms
- In basic igneous rocks. The Finnish spectrolite variety comes from a gabbro intrusion; the Labrador material from an anorthosite complex.
- Chiefly from
- Labrador, CanadaYlamaa, FinlandMadagascar
Why it is that colour
The body colour is dull. The flash — labradorescence — is not colour at all but interference: the mineral separated on cooling into microscopically thin alternating layers of slightly different composition, and light bouncing between those layers cancels and reinforces at particular wavelengths. Tilt it and the colour moves.
Safety
No hazard from handling.
Where it comes from
Madagascar now supplies most commercial material, much of it from small-scale mining with the associated labour concerns. Finnish spectrolite is quarried under regulated conditions and is traceable.
Historical use
A comparatively recent stone in European use, entering the market at the end of the eighteenth century after its discovery on the Labrador coast.
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
Found by Moravian missionaries in Labrador around 1770, so it has no classical or medieval history whatsoever. Inuit tradition in the region associates the stone with the aurora. Everything else attributed to it is modern and mostly post-1970.
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.
Worth knowing
Labradorite is the clearest case in the collection of a name that is not a mineral.
Plagioclase feldspars run continuously from albite to anorthite. In 1988 the IMA formally discredited the intermediate names — oligoclase, andesine, labradorite, bytownite — because they mark arbitrary slices of a continuum rather than distinct species. "Labradorite" now means plagioclase whose composition happens to fall between 50 and 70 per cent anorthite. There is no boundary on either side; the name is a convenience.
None of which makes the optical effect any less remarkable. Labradorescence is a genuine and genuinely unusual phenomenon, and it is structural rather than chemical: the stone is doing to light roughly what an oil film on a puddle does, at a scale you cannot see.
Identity checked against IMA-CNMNC master list, June 2025.