Iolite Meaning: The Viking Sunstone, Explained

What iolite is

Iolite is the transparent, gem-quality variety of the mineral cordierite, a magnesium aluminum silicate from the ring silicate group. The mineral was named in 1813 after the French geologist Pierre Louis Antoine Cordier, who had described it. The name iolite comes from Greek: ion means violet, lithos stone. You will see other names in shops and on old labels. Dichroite, "two-colored," is an older name that points to the color shift. Water sapphire and lynx sapphire are misleading trade names: iolite has nothing to do with sapphire, which is corundum.

Cordierite forms mostly in rocks that were transformed under high temperature, such as gneiss and hornfels. Gem-quality material comes from Sri Lanka, India, Madagascar, Myanmar, Brazil and Tanzania. Cordierite also occurs in North America, including historic finds in Connecticut and in the Canadian Shield, but most of it is cloudy and not worth cutting. In practice, nearly every faceted iolite you can buy in the United States was mined in South Asia or East Africa.

Iolite at a glance

Property	Value
Mineral	Cordierite, a ring silicate
Formula	(Mg,Fe)2Al4Si5O18
Crystal system	Orthorhombic
Mohs hardness	7 to 7.5
Specific gravity	About 2.6, far lighter than sapphire (about 4.0)
Color	Violet-blue, blue, gray; strongly pleochroic
Cleavage	Distinct in one direction
Trade names	Dichroite, water sapphire, lynx sapphire

The color shift: pleochroism

What makes iolite special is called pleochroism, "many colors." Because the crystal lattice is built differently along different directions, it absorbs light differently depending on which way the light travels through it. Iolite shows three tones, depending on which crystal axis you look along: a strong violet-blue, a light blue to gray, and a pale yellow to almost colorless. Many gemstones are slightly pleochroic. With iolite you can see it without a loupe, at arm's length, in ordinary daylight.

For gem cutters this is a challenge. If the rough is oriented wrongly, you look down into the grayish or yellowish direction from the top, and the beautiful blue only shows from the side. A well-cut iolite has its table positioned so the deep blue axis faces up. That is also a quality mark when you buy: a good iolite is saturated violet-blue when viewed face-up, not gray and not washed-out lavender.

The sunstone of the Vikings

In an Old Norse tale, the Raudulfs thattr, King Olaf tests a man's claim that he can tell where the sun stands on a gloomy, snowy day. The king sends for a solarsteinn, a sunstone, holds it up to the sky and sees where light comes out of it. The tale never says what kind of stone it was. In 1967 the Danish archaeologist Thorkild Ramskou suggested it might have been a crystal that makes polarized skylight visible. Even under an overcast sky, light is polarized in a particular pattern relative to the sun, and a birefringent or pleochroic crystal changes brightness or color as you rotate it toward the right direction.

Iolite is a good candidate because its color shift responds strongly to polarized light. The second candidate is Iceland spar, a clear calcite. One find speaks for calcite: in the wreck of an English ship that sank off the Channel island of Alderney in 1592, divers found a calcite crystal lying next to the navigation instruments. Since then, experiments by the research group of Gabor Horvath in Budapest and by French physicists around Guy Ropars have shown that calcite and cordierite really can help estimate the sun's position under cloud, with errors of a few degrees in good conditions. A Viking sunstone itself has never been found. The hypothesis is plausible and tested, but it is not proven.

A note for collectors: what shops sell as "sunstone" is almost always a completely different stone, a feldspar with glittering inclusions. The American version, Oregon sunstone, is the state gem of Oregon and has nothing to do with navigation. The Viking sunstone is a name from a saga, not a mineral species.

Iolite in crystal practice

In contemporary crystal practice, iolite is treated as a stone of orientation and inner sight. The interpretations clearly follow its history: whoever found the way through fog with it should also get direction in a figurative sense. It is assigned to the third eye chakra, is said to support intuition, clarity and imagination, and is used in meditation, dream work and before decisions. Some authors also credit it with physical effects, for example on sleep or headaches. There is no evidence for that, and symptoms belong with a doctor.

As a meditation stone it works through what you bring to it. Its color changes when you change your angle. It is hard to think of a better image for inner work: the same situation looks different depending on where you stand, and you can practice noticing where you are standing right now.

Real or not? How to recognize iolite

Iolite is inexpensive enough that it is rarely faked outright, but it gets confused with other blue stones and is sometimes replaced by glass. Four checks help:

• Turn it. Hold the stone over a sheet of white paper and rotate it. Genuine iolite shifts clearly between violet-blue and yellow-gray. Blue glass stays blue from every angle.
• Tanzanite. Tanzanite is pleochroic too (blue, violet, bronze), but softer at 6 to 7 and far more expensive. A "tanzanite" at an iolite price is suspicious; the reverse is rare.
• Sapphire. Blue sapphire is harder (9), heavier and shows only weak pleochroism. "Water sapphire" on a label means iolite.
• Inclusions. Natural iolite often has fine fractures or veils. Perfectly clean, evenly blue material with round bubbles points to glass.

Iolite, tanzanite, sapphire or glass?

Stone	Hardness	Color change when turned	Price signal
Iolite	7 to 7.5	Strong: violet-blue to gray to pale yellow	Affordable
Tanzanite	6 to 7	Strong: blue, violet, bronze	Several times the price of iolite
Blue sapphire	9	Weak	Expensive, and noticeably heavy in the hand
Blue glass	5 to 6	None	Cheap; often with round gas bubbles

Iolite is generally not treated, and synthetic iolite plays practically no role in the jewelry trade. If you want a broader sense of what gets dyed, heated or coated in the crystal market, our guide to real versus treated crystals walks through the common cases.

Care

With a Mohs hardness of 7 to 7.5, iolite is fine for everyday wear, but it has a distinct cleavage: a hard knock in the wrong direction can split it. Take iolite rings off for gardening, the gym or moving furniture. Clean it with lukewarm water, a drop of mild dish soap and a soft toothbrush; skip ultrasonic and steam cleaners because of possible fractures. It is lightfast, so it will not fade on a sunny windowsill. How it compares with other stones is laid out in our Mohs hardness guide. If you like to clear stones energetically as well, the gentle methods in how to cleanse crystals all suit iolite; avoid salt soaks, which do nothing for the stone and can dull settings.

Three ways people meet iolite

In the world of stones, iolite appears in three roles. For gem cutters it is the stone on which you learn orientation: put an iolite on the dop the wrong way and you throw away its color. For physicists and archaeologists it is an experimental object: the Budapest and Rennes experiments with cordierite and calcite are among the most cited studies on historical navigation. And in crystal practice it is a quiet meditation stone that rarely takes center stage and often sits on the altar next to amethyst or lapis lazuli. What all three roles share is the same kind of wonder: a stone that becomes a different stone depending on how you look at it.

What we don't promise

We do not claim that iolite heals, relieves headaches, improves sleep or awakens clairvoyance; there is no evidence for any of that. We do not claim the Vikings demonstrably navigated with iolite; that is a well-tested hypothesis, not a find. And we cannot promise that every stone sold as iolite is one. Use the turn test.

Practically: how to work with it

• Buy face-up. A good iolite is saturated violet-blue from the top, not gray.
• Do the turn test. Rotate it slowly over white paper. A visible color shift means it is very likely iolite.
• Try the sunstone principle yourself. On an overcast day, hold a clear iolite up to the sky and rotate it. With some patience you will see its brightness change as it lines up with the polarization of the skylight. That is the whole idea behind the Viking hypothesis, in your own hand.
• Protect it from knocks. Take rings off for manual work and store iolite apart from harder stones.
• Work with the image. Use iolite as a meditation anchor. Pick it up when you face a decision and ask yourself which direction you are looking from.

Frequently asked questions

What is iolite?

The transparent, gem-quality variety of the mineral cordierite, a magnesium aluminum silicate. The name comes from the Greek word for violet.

Why does iolite change color?

Because of pleochroism: the crystal lattice absorbs light differently in different directions, so the stone looks violet-blue, light blue to gray, or pale yellow depending on the angle.

Did the Vikings navigate with iolite?

That is a hypothesis. A saga mentions a sunstone, and experiments show that cordierite and calcite can help locate the sun under cloud. No Viking sunstone has been found.

Is water sapphire a sapphire?

No. Water sapphire is a trade name for iolite. Sapphire is corundum, harder and heavier, and not related to iolite.

What chakra is iolite associated with?

In modern crystal practice, usually the third eye, as a stone of intuition and orientation. No effect has been demonstrated.

How do I clean iolite?

Lukewarm water, mild soap and a soft brush. Skip ultrasonic and steam cleaners and avoid hard knocks, because iolite has a distinct cleavage.

Sources and further reading

• Mindat.org: Cordierite, mineral data and localities.
• Gemological Institute of America (GIA): Iolite description and gem quality factors.
• Thorkild Ramskou, Solstenen, Copenhagen 1969 (the sunstone hypothesis, first proposed in 1967).
• Guy Ropars et al., "A depolarizer as a possible precise sunstone for Viking navigation," Proceedings of the Royal Society A 468 (2012).
• Albert Le Floch et al., "The sixteenth century Alderney crystal: a calcite as an efficient reference optical compass?" Proceedings of the Royal Society A 469 (2013).
• Gabor Horvath and colleagues, sunstone navigation experiments with calcite and cordierite, Royal Society Open Science (2016, 2018).
• Raudulfs thattr, Old Norse tale, 14th century.
• More in the magazine: Mohs hardness · Third eye chakra · Cleansing crystals · Real vs treated crystals

Crystal traditions are described here as traditions. Nothing in this article is medical advice. Questions about an order: 28@templeofdesire.com.