Moonstone and labradorite — what's the difference

“Labradorite,” “black labradorite,” “black moonstone” and “rainbow moonstone” sit in neighbouring display cases like four different products, though three of those names usually hide the same mineral. The confusion comes from trade catalogues, where gem names grew up haphazardly, and the seller only passes it along, since beads arrive already labelled by the supplier.

One family of minerals, two different glows

The difference between moonstone and labradorite starts in the chemistry, because both belong to the feldspars, the commonest group in the Earth’s crust, but took different branches inside it. Moonstone in jewellery is adularia, a translucent potassium feldspar, while labradorite is a plagioclase, where sodium gives way to calcium along a series, and it sits exactly in the middle of that series. Their density differs too, around 2.7 g/cm³ for labradorite against 2.56–2.59 for adularia.

Moonstone’s glow is called adularescence, and it is born inside the crystal, where orthoclase and albite lamellae interleave in layers a fraction of a micron thick. Light scatters on those layers, the blue end scatters hardest, so the best stones give a cool blue haze, and thicker-layered ones shine milky white. The haze seems to hang below the surface and barely fades, however you turn the stone.

In labradorite the colour comes from interference, because its lamellae are thicker, hundreds of nanometres, and waves reflected from neighbouring layers add up or cancel out. The colour that flares depends on the thickness of each stack, so blue, green, gold and copper can live in one stone and replace one another as it turns. Adularescence looks like fog under the surface, while labradorescence behaves like a switch that trips within ten or twenty degrees of rotation.

The mineral is named after the Labrador peninsula, where the first samples were found in 1770, and moonstone after the moon its glow resembles. Hardness is identical, 6–6.5 on the Mohs scale, so a scratch test will not tell them apart. Both inherited the common feldspar weakness, cleavage along flat planes, so a knock against a doorframe leaves a step instead of a scratch.

Four names in one display case

Of the four tags, “black labradorite” raises the fewest questions, though mineralogy knows no such variety either. The trade uses it for ordinary labradorite with a dark ground, where blue and green flashes read sharper than on a pale one. The name describes the base colour, and in jewellery it turns up more often than the pale kind.

The mineral and the rock

In mineralogy the stone is one thing and labradorite rock another, built mostly from its crystals and cut into cladding slabs, plinths and gravestones. In the trade the line has worn away, because English catalogues write labradorite for everything, while the Russian tradition we keep on our tags names the mineral alone. On adjacent stalls of the same market you will find both words above identical beads. The price gap comes from the iridescence, the size of the flash and the clarity of the ground beneath.

Two “moon” names with borrowed ancestry

“Black moonstone” was invented by suppliers, who sell dark feldspars with a soft sheen under that name, most often from Madagascar. Chemically it is usually plagioclase, labradorite’s nearest relative, so it has nothing to do with adularia, though the word “moonstone” sits there on the tag.

“Rainbow moonstone” is almost always pale labradorite, whose translucent whitish ground with flashes resembles adularescence just enough for the name to stick for good. Beside these trade names it is worth remembering spectrolite, the Finnish labradorite from around Ylämaa, found in 1940 during the building of fortifications. Its colour range is the fullest of all, red included, and it costs noticeably more than ordinary dark material.

How the two stones share one look

Side by side they work on contrast, because dark labradorite holds the composition and pale adularia thins it. Two stones of a similar tone cancel each other, since the flash needs a dark ground and the adularia glow needs air around it. Warm brass draws out the gold and copper flares, while cool steel supports the blue light of adularia. We work with both metals and keep no others in the workshop.

The “KHALISI majestic” bracelet at 22,000 ₽ sets labradorite next to moonstone on a brass base. In the “Spheres” ring at 5,500 ₽ the same two minerals sit beside rose quartz on three steel spheres. The “Dragon Wing” necklace at 39,000 ₽ is all labradorite, and on a multi-strand piece you see clearly that the beads do not light up at once. All three we assembled by hand, one at a time, there is no second copy in stock, and two strands cannot match by physics, since neighbouring cleavages of one crystal give different colours.

Both stones ask for the same care, a soft dry cloth and taking the piece off before water and housework. The velvet pouch it arrives in works for storage at home, because feldspar does badly next to harder stones. What exactly ruins the polish is set out in our care guide and in the article on caring for natural stones.

Their meanings parted ways as well, because moonstone is traditionally believed to carry softness and intuition, and labradorite protection and readiness for change. These ideas live in culture and lithotherapy, whereas no verifiable effect on health has ever been shown. Both stories are covered in detail in the articles on moonstone and on labradorite.

What you can check at the counter

Telling moonstone from labradorite in a shop takes a minute, and no instruments are needed for it.

• Hold a bead up to the window, because adularia lets light through, while dark labradorite leaves a blank patch.
• Tilt the piece slowly and watch the glow die, since the adularia haze holds at many angles, while labradorite switches off in whole planes.
• Look at the colour, because blue and milky most often mean adularia, while copper and bright green almost certainly give away labradorite.
• Weigh the piece in your palm if the beads are large, because labradorite is noticeably denser than adularia.

No need to scratch or heat the stone, because the hardness is the same and the polish is easy to ruin. Be wary of an even blue sheen, the same across the whole surface and independent of angle, because that is how the glass sold as “opalite” behaves. The same signal comes from a strand where every bead burns at once, since on natural stone half the bracelet always faces away from the light. If the piece is coming from an online shop, ask for a short video of it turning, since in a still photo the iridescence comes out neon or invisible. At the counter one flick of the wrist is enough, and the stone tells you which of the four names is closest to the truth.