Gem Focus – August 2024 – Featuring Ametrine: The intriguing bicolor quartz
*Gem Focus & Market Pulse (Free Subscriber)Bicolor gems are popular in a big way in the current market, and there’s one in particular that offers a wonderful and affordable option in the area: ametrine.
As the name suggests, ametrine is a bicolor quartz featuring the colors of both amethyst and citrine. Fine ametrine shows medium dark to moderately strong orange, and vivid to strong purple to violetish purple. The most intense, saturated colors often show up in larger stones, especially those over 5 carats, according to GIA. Faceted ametrine is generally eye clean.
A 7.21-carat Bolivian ametrine from John Dyer.
(Photo credit: Ozzie Campos)
Dealers, wholesalers, and designers tend to gravitate toward the material that has a distinct contrast between the two colors. It’s often cut in a step cut to best display the bicolor effect with both colors equally displayed, but mixed cuts or brilliant cuts are also employed to use the internal reflections to allow the two colors to mingle. It’s also popular in free-form shapes or fantasy cuts.
Natural ametrine only has one commercial source: the Anahi mine in eastern Bolivia, near the border with Brazil. Legend has it a Spanish conquistador discovered the mine in the 1600s and introduced the gem to Europe, but then the location was lost for more than 300 years. It was rediscovered in the 1960s, and ametrine started showing up in the market again in the 1970s, GIA said. The Anahi mine also produces amethyst and citrine.
This cuff from Atelier Zobel features a 31.63-carat ametrine fantasy cut by Atelier Munsteiner,
and colorless and pink diamonds in 22- and 24- karat gold and sterling silver.
(Photo credit: Atelier Zobel by Peter Schmid)
Natural ametrine’s color zoning is caused by different oxidation states of iron during crystal formation, according to GIA. But it can also be artificially created by heat treatment and/or radiation of amethyst. There is also synthetic ametrine available on the market. Because the latter matches its natural counterpart both optically and physically, gemological testing is needed for identification.
Ametrine comes in a wide range of sizes, the larger pieces being more popular with gem carvers. It’s a very affordable material, even in larger sizes. Since it is readily available in bigger pieces, price per carat stays about the same as size increases for commercial qualities. And, as material increases in size in the good to fine/extra fine quality, price per carat doesn’t increase as dramatically as happens with many other gems.
Ametrine has a refractive index of 1.544 to 1.553, a Mohs hardness of 7, and good toughness. GIA said ametrine can fracture with abrupt temperature changes, and some can fade with prolonged exposure to intense light. It can also be damaged by hydrofluoric acid, ammonium fluoride, and alkaline solutions.
It can be cleaned with warm, soapy water. Ultrasonic cleaners are also usually safe for ametrine, unless the piece has been dyed or fracture filled. Steam cleaning is not recommended.