A moonstone has no color you could really describe. It has a light that sits beneath the surface and moves when you move. The Romans believed it was frozen moonlight. The real explanation is less poetic and at least as beautiful.
Moonstone is the gem variety of the mineral orthoclase, a potassium aluminum silicate from the feldspar family, also known as adularia. As the rock cools, orthoclase and albite separate into extremely thin alternating layers. These layers are the reason for everything that makes the stone what it is.
The moonstone necklace in our Signature collection carries a raw stone from the deposits near Meetiyagoda in Sri Lanka. At about 12 to 14 mm (roughly half an inch), it is the largest stone in the collection. It stays uncut, is wrapped in wire at the top and hangs on a fine chain in 925 sterling silver or 14K gold-filled.
What a moonstone is made of
Orthoclase is a feldspar, and feldspars are the most common mineral group in the earth’s crust. Moonstone is the rare variety in which the layers are fine enough to scatter light. At 6 to 6.5 on the Mohs scale, it is softer than quartz.
“You don’t cut a moonstone to make it more beautiful. You leave it as it is so the light has room.”
I. Moonstone: a member of the feldspar family.
Feldspars make up most of the earth’s crust, and most of them are a plain gray or pink. What sets a moonstone apart from ordinary orthoclase is what happens as it cools: potassium and sodium only share the crystal lattice at high temperatures. When the rock cools slowly, they separate into layers of orthoclase and albite so thin that you have to count them under a microscope.
The moonstone has a close relative in our collection: labradorite, also a feldspar with exsolution layers. In labradorite the layers are thicker and flash blue, green and gold. In moonstone they are so fine that only a white-blue glow remains. Same family, two different ways with light.
II. Adularescence: the light between the layers.
When light enters the stone, it meets thousands of boundaries between orthoclase and albite. At each one, a small part of it is scattered. How it scatters depends on the thickness of the layers: when they are very fine, mostly the blue part of the light is sent back, and when they are thicker, the glow looks white. That is why a bluish moonstone is considered the more desirable one.
The glow does not sit on the surface but beneath it, and it moves as the angle changes. Gemologists call this adularescence, after adularia. This second name of the mineral goes back to the Adula massif in the Swiss Alps. Our moonstone from Sri Lanka shows a milky white body with a cool blue sheen that glides across the raw stone with the light.
The moonstone does not add color. It sorts the light that reaches it.
How the glow forms
The alternating layers act like a stack of semi-transparent mirrors. The light they scatter comes back out slightly offset and creates the floating glow. Turn the stone, the angle shifts, and the glow moves with it.
III. Set raw: why we don’t cut our moonstone.
Lumière Factor · Raw moonstone
23 / 25
Transparency
Clearly translucent, milky white body
20 / 25
Color depth
White base tone with a cool blue sheen
22 / 25
Surface integrity
Intact natural shape, naturally formed fracture faces
24 / 25
Liveliness
Strong adularescence that moves with the light
Total 89 out of 100: Very good. The scale runs from Basic (up to 60) through Good (61 to 75) and Very good (76 to 89) to Exceptional (90 to 100).
A cut moonstone shows its glow in one direction only, where the cutter aligned the layers parallel to the surface. A raw stone has natural fracture faces at different angles. As you move, the light always finds a face where it can float. That is why our moonstone stays raw.
The wire is wrapped around the top of the stone by hand, so the setting follows its natural shape. No two stones are alike, so no two settings are alike. The moonstone is untreated: no heating, no irradiation, no dyeing. Just the way it comes out of the ground.
For the Lumière Factor, we check every stone on four criteria: transparency, color depth, surface integrity and liveliness, each worth up to 25 points. Our moonstone scores 89 out of 100, “Very good,” with its highest mark for liveliness: the glow moves with every motion.
IV. Moonstone, labradorite, cultured pearl: three ways to glow.
Hardness and size compared
Three light effects
Moonstone
Adularescence
Scattering in the finest layers, white-blue glow beneath the surface
Labradorite
Labradorescence
Interference in thicker layers, play of color in blue, green and gold
Pearl
Luster
Reflections from thousands of layers of nacre, a soft shine
Why it matters in the studio
Four promises we make about our moonstone.
01
Genuine and untreated.
No heating, no irradiation, no dyeing. The stone shows the glow it was given in Sri Lanka.
02
Raw, so the light has room.
Natural fracture faces at many angles. The glow travels instead of standing still in one direction.
03
Set by hand.
The wire follows the shape of the stone. No two settings are alike, because no two stones are alike.
04
Water-resistant, but sensitive to knocks.
The necklace can handle water. The stone has perfect cleavage and does not like hard knocks, heat or ultrasonic cleaners.
The next time you hold your moonstone necklace up to the light, turn it slowly. The glow that drifts across the stone is not a surface trick. It comes from millions of tiny boundaries that formed long ago in Sri Lanka and have been waiting for light ever since. How to care for the stone is covered in our post on jewelry in summer.
No stone shines by itself. It just lets the light take a different path.
Carola
The raw moonstone is the birthstone for June, available in 925 sterling silver or 14K gold-filled.
View the Moonstone Necklace
