Let's Take a Deep Dive Into the Optical Phenomenon Called 'Chatoyancy'

This 58.19-carat, honey-colored "Maharani Cat’s Eye" displays one of the world's finest examples of an optical phenomenon called "chatoyancy" — or the cat's eye effect.

A chatoyant gem presents a single band of reflected light that seems to move just beneath the surface of the stone, and the effect looks very much like the vertical-slit pupils of a cat's eye.

Chatoyant is derived from the French word "chatoyer," which literally means "to shine like a cat's eyes."

Chatoyancy arises when light reflects off of needle-shaped inclusions present within the body of the gemstone, in this case chrysoberyl. When a stone is cut with a domed top and flat bottom, called a cabochon, the light reflected off the inclusions is focused into a bright band that forms the "eye." To get the best results, cutters will orient the needle-shaped inclusions to be parallel to the base of the gem.

When the needles are oriented in a single direction, the result is a cat's eye. When the needles grow in three directions, the result will be a six-rayed asterism or "star."

Chatoyancy occurs in many gemstone varieties, including corundum, tourmaline, spinel and quartz, but the most coveted cat's eyes are cut and polished from the mineral chrysoberyl.

The International Gemological Institute clarified that while other minerals can be polished to produce a similar cat’s eye effect, only chrysoberyl can be referred to as “cat’s eye” with no other designation. Other minerals require a qualifier, such as cat’s eyes quartz or cat's eye sapphire, etc.

The stone seen above was sourced in Sri Lanka and is now part of the Smithsonian's National Gem Collection. The Smithsonian obtained the gem in an exchange in 1961.

Credits: Gem photos by Chip Clark / Smithsonian. Cat's eye by Keith Kissel, CC BY 2.0, via Wikimedia Commons.

5.09-Carat Paraiba Tourmaline Stars at Bonhams' Hong Kong Auction

An impossibly rare 5.09-carat electric blue Paraiba tourmaline fetched $377,650 at Bonhams' Jewels and Jadeite auction in Hong Kong last night.

The modified shield brilliant-cut gem was the most anticipated lot of the event because a stone of this color, size, quality and origin is a unicorn in the world of colored gemstones. Faceted specimens larger than a few carats are virtually unheard of.

To put the rarity of such a large intense blue Paraiba tourmaline into some perspective, note that the Smithsonian has one in the National Gem Collection in Washington, DC. It's an oval-cut gem and weighs a mere 1.22 carats.

"Paraiba" is the most prized tourmaline variety. The vivid teal, turquoise and neon blue stones caused a sensation when they were first discovered by prospector Heitor Dimas Barbosa in Brazil’s tropical, coastal state of Paraiba in 1989.

Worldwide demand sparked a mining frenzy and, within five years, the supply beneath “Paraiba Hill” — an area measuring 400 x 200 x 65 meters — was largely tapped out.

Bonhams explained that Paraiba tourmalines are typically seen in smaller carat sizes because the crystals mined at their original source were extracted from pencil-thin veins. The material was delicate and prone to splintering or fragmenting during the mining process.

Common tourmalines come in a rainbow of colors, which are determined by the trace amounts of iron, manganese, chromium or vanadium in their chemical makeup. Paraiba tourmalines are different. They owe their spectacular blue hues to a high concentration of copper, an element not previously seen in tourmalines.

Bonhams noted that while traditionally mined in Brazil, copper-bearing tourmalines have been discovered in both Mozambique and Nigeria.

Some gem experts believe that the uncanny connection can be attributed to continental drift, the theory that the Earth’s continents have moved over geologic time and that South America and Africa were once connected. Paraiba, on the far eastern tip of Brazil, would have been adjacent to the west coast of Nigeria.

“Thus we may suppose that the radiant copper tourmalines from Nigeria came into being under the same conditions as those from Paraiba, at a time before the ancient continent drifted apart,” writes the International Colored Gemstone Association on its Paraiba Tourmaline web page. “Is that the reason why it is so difficult to tell one from the other? This remains one of the great riddles in the fascinating world of gemstones.”

Credit: Image courtesy of Bonhams.

Bedazzled Basketball Becomes Unofficial Mascot of NBA's Diamond Anniversary

Exactly a week after the Golden State Warriors put an exclamation point on the NBA’s 75th Anniversary season by defeating the Boston Celtics in the Finals, the basketball association's senior director of social media, Ashley Atwell, revealed the backstory of how a bedazzled basketball became the unofficial mascot for NBA 75.

It all started with a fresh take on the NBA's iconic NBA logo, which features a silhouette of former LA Laker and Hall of Famer Jerry West. For the league's diamond anniversary season, the NBA "Logoman" was reimagined in the center of a blue and red diamond with the number 75 superimposed over facets rendered to mimic the seams of a basketball.

“It was the NBA’s diamond season, so we took that theme of the diamond logo while creating the ball,” Atwell told NBA.com. “The idea was sparked because we previously used the bedazzled ball at an award show. This was a really good opportunity to bring that idea back to life. So, once we saw the logo, we thought it would be cool to put it on a ball. This really started because we needed a cool idea for the NBA Draft.”

All the draftees who were in Brooklyn last July got to take a pic with the gem-encrusted ball. And slowly but surely, the ball started making appearances everywhere.

It appeared at the G League Winter Showcase, NBA All-Star Weekend, Formula One Grand Prix and NBA venues throughout the country. There was so many requests for the ball that the league decided to create eight additional promotional balls to fill the demand.

We're guessing that the white, red, blue and black stones affixed to the "diamond" balls are actually glass crystals.

Atwell challenged fans to search for the NBA 75th Anniversary ball on Tik Tok, Instagram or Twitter. The results will be collection of celebrities, players and fans of all ages posing with the ball.

“The celebrities are cool,” Atwell said. “There are definitely moments where you’re like, 'Oh my God, I can’t believe that celebrity had the ball.’"

Atwell said that actor Kevin Hart was the first to post to IG a picture of himself with the ball. Then there was a photo of former Indiana Pacers star Reggie Miller sharing the ball with actor-director (and NY Knicks fan) Spike Lee.

"The ball has become the face of the 75th anniversary, especially on social media," said Atwell. "It’s a big part of the campaign. I don’t think I realized that was going to happen."

Atwell said that she remembers pitching the diamond ball idea in preparation of the 75th anniversary season. At the time, she said, it seemed insignificant in the grand scheme of things.

Now, in retrospect, she acknowledged that the diamond ball evolved into one of the biggest fan-facing initiatives of the season.

"It’s helped us carry the campaign all season long," she said. "And bring these generations together – fans and players.”

Credits: Houston Rockets rookie Jalen Green with the 75th anniversary ball, photo courtesy of the NBA. Logos via NBA.com.