silicates
Moonstone
- Also known as
- adulariarainbow moonstone
- Crystal system
- monoclinic
- Hardness
- 6–6.5 on the Mohs scale
- Lustre
- vitreous
- Colour
- Colourless to white, with a floating blue or white sheen
- Where it forms
- In pegmatites and in some metamorphic rocks, where a single feldspar cooled slowly enough to unmix into alternating lamellae.
- Chiefly from
- Sri Lankasouthern IndiaMadagascarMyanmar
Why it is that colour
Adularescence — the same mechanism as labradorescence. Intergrown microscopic layers of orthoclase and albite scatter light, and because the layers are thin the scattering favours blue. The glow appears to sit below the surface and moves as the stone tilts.
Safety
No hazard from handling. Feldspar cleaves readily, so it chips more easily than its hardness suggests.
Where it comes from
Sri Lanka has been the classical source for two thousand years and its best blue material is now scarce. Most inexpensive "rainbow moonstone" is white labradorite, not adularia, and is a different material sold under a borrowed name.
Historical use
Named adularia after the Adula massif in Switzerland. Enormously fashionable in the Art Nouveau period, when Lalique and Tiffany used it extensively.
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
Roman writers connected it with the moon and believed it waxed and waned with the lunar cycle; Pliny records this. Indian tradition treats it as a sacred stone and it appears in Sanskrit sources. The association is therefore genuinely ancient in two independent traditions, which is unusual. Its specific modern role in fertility and cycles is a twentieth-century elaboration.
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
Moonstone is one of the small number of stones where the classical association and the modern one point the same way, and it is worth asking why. The answer is almost certainly that the resemblance is doing the work: a pale stone with a soft light moving inside it looks like the moon, and two unconnected traditions reached the same image independently.
That is a reasonable account of how correspondences form, and it is not mystical. It also explains why the correspondences are so often about appearance — bloodstone for bleeding, moonstone for the moon, amethyst for wine-coloured sobriety. What it does not explain is why any of them should work.
Identity checked against IMA-CNMNC master list, June 2025.