Labradorite
Labradorite doesn’t have a single chemical formula, and that’s not an oversight — it’s a genuine feature of what the stone is. It belongs to the plagioclase feldspar group, a solid-solution series that ranges continuously between two end members, albite (sodium-rich) and anorthite (calcium-rich), with labradorite occupying a specific band in the middle of that range. Because any given piece can sit anywhere within that band, there’s no fixed composition to write down, only a range — the same reason no crystal-system-defining formula appears on this page where other feldspar-family or single-species stones would have one.
What labradorite is known for has nothing to do with its body color, which on its own is often an unremarkable gray. The dramatic flashes of electric blue, green, and gold that make it prized are caused by labradorescence, an optical interference effect produced when light bounces between microscopically thin internal layers within the crystal structure — similar in mechanism to the shimmer in some moonstone, another feldspar whose visual effect (adularescence, in that case) also comes from internal structure rather than pigment. Tilt a labradorite stone out of the right angle and the color can vanish almost entirely, which surprises people expecting a gem’s color to be constant.
At Mohs 6 to 6.5, labradorite is moderately durable — softer than quartz, harder than most carbonate ornamental stones — and crystallizes in the triclinic system, the least symmetrical of the crystal systems, consistent with its feldspar relatives. Its refractive index runs 1.559 to 1.573. Canada, particularly Labrador (the region the stone is named for), is a classic source, alongside Madagascar, Finland, and Russia, with Finnish material — sometimes marketed as “spectrolite” — known for an especially broad flash spectrum.
Because it belongs to a series rather than a single defined species, labradorite is distinguished from its plagioclase relatives mostly by where it sits along the albite-anorthite range and by the visible presence of labradorescence — material from the same compositional range without a strong flash is sometimes simply called gray or andesine labradorite instead, depending on locality and trade convention. That fuzziness at the edges is a direct consequence of being a series rather than a fixed compound, not a labeling inconsistency.
Labradorite doesn’t appear on any of the historical or modern monthly birthstone lists, or on either zodiac system, tracked on this site — it’s included here purely as a standalone gemstone reference entry.
Gemmological properties
| Mohs hardness | 6–6.5 |
|---|---|
| Crystal system | Triclinic |
| Chemical formula | Not recorded |
| Refractive index | 1.559–1.573 |
| Color family | Gray, Blue, Multicolor |
| Variety of | plagioclase feldspar |
| Also known as | — |
| Origins | Canada, Madagascar, Finland, Russia |
| Organic material | No |
Labradorite is a plagioclase feldspar, a solid-solution series between albite and anorthite rather than a fixed composition, so no single formula applies. Its flashes of blue and gold ("labradorescence") are an optical interference effect from internal layering, not body color — the stone itself is an unremarkable gray when the light is wrong.
Frequently asked questions
- Why does labradorite have no chemical formula listed?
- Because it isn't one fixed compound. Labradorite is a plagioclase feldspar, part of a solid-solution series between albite and anorthite, meaning its exact composition varies continuously between those two end members rather than settling on a single formula — so no single formula applies.
- What causes the blue and gold flash in labradorite?
- Labradorescence, an optical interference effect caused by light bouncing between microscopic internal layers within the crystal. It's a structural effect, not a body color — turn the stone so the light doesn't hit those layers correctly and it can look like plain gray stone.
- Is labradorite a birthstone on any of the lists this site tracks?
- No. It doesn't appear on any of the historical, US, UK, or zodiac systems documented on this site — it's covered here as a standalone gemstone reference entry.