Iolite Buying Guide
Soft, violet-blue hues have made iolite a popular stone. Sometimes mistaken for better-known sapphire or tanzanite, top-color iolite is a rare treat. This gem variety of cordierite shows strong pleochroism. Researchers believe this stone may have been one of the first polarizing lenses. The Vikings may have used this feature to find the Sun on a cloudy day, allowing them to navigate the northern seas.
Today, this gem is rapidly growing in popularity due to its color and affordability. Since iolites have no known color treatments, buyers can be confident their purchases are unenhanced.
Learn more about the quality factors for this trendy stone before your next iolite buying trip.
Iolite Buying and the Four Cs
The IGS iolite value listing has price guidelines for top-color cut stones and cabochons as well as for colorless gems.
Iolite, from the Greek for “violet stone,” is most valuable with a slightly violet-blue face-up color. This hue causes some consumers to confuse iolite with sapphire or tanzanite, two stones of much greater rarity and value. However, most iolite has a washed-out or inky look, and few gems exhibit high saturation. For highly saturated iolite, the ideal tone is medium-dark.
Rare colorless stones have prices only somewhat less than a top-color violet-blue iolite.
Iolite is strongly pleochroic, exhibiting different colors along its different crystal axes. When tilted or viewed from the side, an iolite gem that appears blue from the top may be nearly colorless, gray, or pale yellow.
Some consumers may prefer a cut and setting that shows off the gem’s pleochroism, while others will prefer a setting which hides it to appear more like a classic blue sapphire.
Eye-clean iolite is abundant. Therefore, iolite set in jewelry shouldn’t have any visible inclusions. The most common inclusions are long, tube-like structures which can create a cat’s eye or, more rarely, a 4-rayed star. Stones with these unusual effects may also make attractive cabbed pieces.
Due to its strong pleochroism, orienting iolite properly for best color is difficult for gem cutters. Furthermore, its cleavage poses additional problems. Still, due to its abundance, well-cut iolite is readily available. Dark rough may have a window or a shallow cut to lighten the gem.
High-quality material can be found in sizes up to ten carats. Stones above 15 carats with good color and clarity are museum pieces.
For this gem, price per carat jumps at one and ten carats.
“Bloodshot” iolite contains hematite inclusions. In a properly cut stone, these inclusions can create attractive sparkles.
At 7.0-7.5 on the Mohs scale, iolite is a hard stone and will resist scratching. However, it’s prone to fracture. As a result, iolite is best suited for use in jewelry such as pendants, brooches, and earrings. Protective jewelry settings can also help prevent fracture.
In addition, iolite is heat sensitive and shouldn’t be subject to heating during setting. Similarly, steam cleaning may damage the stone.