Everything you need to know about Iolite Gemstone

According to folklore, ancient Viking navigators used iolite filters made from thin slices of stone to find the sun on overcast days. Whether or not the stories are accurate, Jewellery made from Iolite can be pretty stunning. Furthermore, Cordierite is another name for Iolite in the mining industry.

Iolite gemstone


Iolite is commonly mislabeled as "water sapphire" due to its strong pleochroism, which causes it to seem either blue or violet in one direction or pale yellow or colourless in the other.


According to various beliefs, Iolite helps people to fall asleep and opens their minds to new ideas. Many sources, however, recommend Iolite as a gift for a twenty-first anniversary.

The intense pleochroism of Iolite makes it challenging to achieve a high-quality gem cut.  However, this aluminium-iron-magnesium silicate has a stunning pleochroism that is easily visible to the naked eye. Moreover, its attractive violetish blue to slightly violetish blue colouration originates from the iron content.

Iolite gemstone


It has a pleochroic pattern on its body that doesn't match its skin colour. Therefore, Iolites are typically seen as violet and exhibit a pleochroic colour scheme of violet, dark violet, and yellow-brown. 

However, Iolites with a blue hue have pleochroic colours ranging from colourless to yellow to blue-grey to deep violet. So, a bluish iolite can look yellow or even colourless from some perspectives, whereas a violet iolite can look brown.

Iolite rates at a 7–7.5 on the Mohs scale. However, its fair toughness is due to its noticeable cleavage in one direction. Due to this, Iolite is prone to breaking when used in Jewellery such as rings or other settings subjected to everyday use.

Iolite is rarely processed, in contrast to tanzanite. Fine Iolite acquires its enticing blues and violets in a completely natural process. Since most blue stones, from inexpensive blue topaz to high-quality Sapphire, are cut and polished, its lack of such treatment is a selling point.

Iolite doesn't always display good colour, of course. Some gems may appear nearly colourless or grey. The trade would do so if it could alter these less desirable iolites to give them a better, more marketable tint. But the chemistry of Iolite prevents it. 

It is interesting to note that the blue in Sapphire and the deep blues of some iolites may have the same source. Unfortunately, unlike Sapphire, Iolite's low melting point means it cannot be heat-treated to deepen its blue hue in the same way as corundum is.


Absorption Spectrum Pleochroism Cleavage
Iron spectrum. Weak bands at 6451, 5930, 5850, 5350, 4920, 4560, 4360, and 4260. The spectrum observed varies with the direction of the crystal. Intense and distinctive. Fe-rich crystals: a = colorless; γ = violet. Mg-rich crystals: pale yellow to green/pale blue/violet, violet-blue. Distinct one direction
Birefringence Phenomena Colours
0.005-0.018 Chatoyancy, asterism (very rare). Blue, slightly violet blue, grey, near colourless
Refractive Index Crystallography Specific Gravity
1.522-1.578 Orthorhombic. 2.53-2.78
Special Care Instructions Dispersion Transparency
None 0.017 Translucent to transparent.
Enhancements Variety of Fracture
None. Cordierite Conchoidal to uneven
Formula Wearability Mohs Hardness
(Mg, Fe2) Al4Si5O18 Very Good 7-7.5
Mineral Heat Sensitivity Lustre
Iolite/Cordierite No Vitreous.
Luminescence Present Luminescence Optic Sign
No None. Biaxial +, Biaxial -


Iolite, also known as Viking Compass Stone, is present in mythology. According to legend, polarising filters and glare-reducers constructed from thin slices of Iolite may have helped ancient Viking navigators find the sun on cloudy days. Moreover, the Nordic seafarers could determine their exact location on the water because of the Iolite.

Tanzanite is another translucent, pleochroic, violet-blue gem that has been around for thousands of years. Therefore, at first, gemologists thought tanzanite was Cordierite. Yet Iolite has not yet gained as much popularity among merchants as tanzanite did in the 1970s and 1980s.

Iolite gemstone rough state


Iolite was formerly known as Cordierite after the French geologist Pierre Cordier. However, 'Iolite,' derived from the Greek word 'ios,' meaning 'violet,' is the most common commercial term for Cordierite today.

It is common to find Iolite in alluvial deposits because of its relative hardness. Iolite can be found in several locations across Africa, not just in the gem gravels of Sri Lanka. India, Brazil, and Norway are all essential producers of this mineral. Furthermore, Madagascar hosted a major iolite find in 1994.

However, according to experts, there isn't yet a steady enough supply of uniformly fine-quality Iolite available for jewellery designers and retailers to feel secure ordering a wide variety of materials for their workshops and stores.

Stone Size

It is common to practise cutting iolites into faceted gemstones, but cabochons are also popular. A finished piece of Iolite can be anything from one carat to ten carats in weight. However, Iolites that are so fine that they weigh more than 5 carats are incredibly uncommon.

Iolite gemstone


Stone Care

If you want to clean your Iolite, use warm, soapy water rather than steam or ultrasound. As Iolite is typically not a treated stone, coatings and dyes are seldom a problem with this gemstone. Protect your Iolite from any sharp hits that could cause it to crack along its natural cleavage planes.

Iolite gemstone care ring



1. What is Iolite known for?

The glare from the sun could be annoying when checking its position. Thus the Vikings supposedly utilised iolite slices for this purpose. Colour changes occur in Iolite when seen from different angles. Therefore, faceting an iolite stone is a common way to show off the gem's innate clarity.

2. Is Iolite an expensive stone?

It's not hard for your wallet to buy an iolite. More commonly found and more reasonably priced are fine stones weighing between 1 carat and 5 carats. However, stones with a carat weight of 5-10 are more expensive than smaller ones but still less than other blue gems like tanzanite or Sapphire.

3. Is Iolite the same as Sapphire?

Iolite, like Sapphire and tanzanite, is a pleochroic blue gemstone. It may stand in for either of those precious stones and is far more affordable. Therefore, the gem industry does not treat Iolite with heat or radiation to enhance its colour, as with Sapphire and tanzanite.

4. Does Iolite scratch easily?

Iolite is a relatively 'hard' stone on the Moh's scale of mineral hardness. Therefore, Jewellery made with it is unlikely to harm other items of Jewellery while being worn or stored. Iolite is a beautiful stone but fragile and can shatter if bumped incorrectly.