Tuesday, 23 May 2017

Alexandrite

Described by gem aficionados as “emerald by day, ruby by night,” alexandrite is a very rare color-change variety of the mineral chrysoberyl.

Alexandrite deposits were first discovered in 1830 in Russia’s Ural Mountains. Those first alexandrites were of very fine quality and displayed vivid hues and dramatic color change.
The spectacular Ural Mountain deposits didn’t last, and today most alexandrite comes from Sri Lanka, East Africa, and Brazil. The newer deposits contain some fine-quality stones, but many display less-precise color change and muddier hues than the nineteenth-century Russian alexandrites.

Fine alexandrite is green to bluish green in daylight and red to purplish red in incandescent light. Alexandrite is most often available in mixed cuts. Its extreme rarity means it is often cut to save weight.
Good quality alexandrite has few inclusions. Rarely, needle-like inclusions create a cat’s-eye. Most cut gems weigh less than one carat. Larger, high quality gems rise in price dramatically.

Production from Russian mines is very limited today. Sri Lankan alexandrites are generally larger but their colors tend to be less desirable. Alexandrites from Brazil have been found in colors that rival the Russian material, but production has decreased.

Martin Katz - Jewels. Like No Other


Australian black red opal ring set in 18K white gold; micro-set with 234 white diamonds and 377 red and orange sapphires, 36 tsavorite garnets and 5 green tourmalines.
For over 25 years, Martin Katz has married exquisite gemstones with meticulously designed settings to create extraordinary jewelry.

Katz, 58, has long had a passion for gems. In college, he built a small business selling puka shell and silver jewelry to sorority girls. After graduation, he moved to California and began working in the trade.

Eventually, he launched himself as a private jeweler. Becoming a designer wasn’t part of the plan. “Designing came out of filling a void,” he says, for clients seeking a specific piece to round out a vintage collection. “I’d say, ‘If we could make one, we’d take the top of this one and the shape of that one.’ That’s how it all started.”

His reputation grew, and before long, his contemporary designs were selling better than the vintage.


White gold ring with a 4.25ct oval pinkish orange padparadscha sapphire, microset with diamonds and pink sapphires.
Katz’s pieces start at $2,500, but the core artistic collection ranges from $25,000 to $125,000.

He’s especially known for his expertise in colored stones; paraiba tourmaline, red spinel, alexandrite, and notes that pink and yellow diamonds are trending higher.

Cushion-cut Mandarin garnet of 10.25 carats encircled by a micro-set border of orange sapphires and band with white diamonds with 2 half-moon diamond sidestones.

Cushion-cut orange sapphire, 15.5 carats; set in 18K white gold, micro-set with 118 amethysts and 98 diamonds.

Cushion-cut sapphire, 10.95 carats; microset with 128 diamonds and 64 blue sapphires. Set in platinum.

Cabochon fire opal, 13 carats; 354 diamonds, 14 green tsavorite garnets and 179 orange-red sapphires. 18K white gold setting.

Diamond ring bought for £10 worth $ 450,000

A woman bought the 26.27-carat cushion-shaped white diamond ring at West Middlesex Hospital in Isleworth, west London, in the 1980s. She wore it every day for three decades, as she assumed it was not a genuine gemstone.

The woman had assumed the ring wasn't worth much due to its shape, cut and lack of sparkle. “With an old style of cutting, an antique cushion shape, the light doesn't reflect back as much as it would from a modern stone cutting. Cutters worked more with the natural shape of the crystal, to conserve as much weight rather than make it as brilliant as possible.”

The gem is expected to fetch about 350,000 pounds ($454,000) when it is auctioned by Sotheby's next month.

Sunday, 21 May 2017

Andalusite

Andalusite is an aluminum silicate closely related to both sillimanite and kyanite. All three minerals are polymorphs. They share the same chemical composition, but possess different crystal structures. Andalusite is a strikingly beautiful gem, but it is one of the lesser-known gem types in the trade.
Andalusite gemstones are found in very distinct combinations of colors, with a very pronounced level of pleochroism.

New-found appreciation for andalusite is greatly owed to its unmistakable and unique twist on play of color. For many years andalusite has primarily been a collector's stone, but it has recently gained attention from jewelry designers.

It is an ideal hardness, about 7.5 on the Mohs scale.

Friday, 19 May 2017

Demantoid Garnet

Demantoid is the green gemstone variety of andradite, a member of the garnet group. Andradite is a calcium-and iron-rich garnet with the formula Ca3Fe2(SiO4) with chromium the cause of the demantoid green color. Ferric iron is the cause of the yellow in the stone. Demantoid garnet was first discovered in 1886 and became a favorite of Russian royalty and designer Carl Fabergé, who incorporated them into his jewelry.
Russian mining of demantoid garnet was suspended after the Bolshevik Revolution in 1917, but resumed in the 1970s.
Demantoid gets its name from the Dutch words for “diamond-like.” The stone owes its impressive brilliance to two main factors: A high refractive index and a high dispersion. Demantoid’s dispersion rating is the highest of all gemstones, including diamond. Known for their brilliant green color and fiery dispersion, demantoid garnets are unique because their inclusions — usually seen as flaws in other gems — are considered highly coveted aesthetic attributes.
Demantoid garnet is mined in other parts of the world, including Iran, Namibia, Pakistan, Italy, Madagascar and Canada, but Russian demantoid sets the mark by which all the others are compared. Demantoid garnets are rarely found in sizes larger than 2 carats.

Bonhams’ Rare Jewels & Jadeite Auction

Among the leading items on sale is a pair of emerald and diamond earrings; emeralds weighing in at more than 10 carats are a rarity, so to get two of 10.91 and 10.26 carats in a pair partly explains the estimated HK$3.8-4.8 million price.

The pair of Namibian fancy coloured diamond and diamond earrings from Forevermark are estimated at $2.3-2.8 million. The earrings feature two asscher-cut fancy intense yellow diamonds, weighing 5.26 and 5.17 carats.
A ruby and diamond bracelet, with an estimate of $2.3-2.8 million, features 30 vivid red pigeon-blood cushion-shape examples from Myanmar with a combined weight of 30 carats.

A step-cut 10.06 carat ruby set in a tsavorite garnet and diamond ring comes from Kenya. Set within a surround of pavé-set circular-cut tsavorite garnets and diamonds, it is estimated $1.5 million and $2 million.

Australian Black Opal and Diamond Pendant Necklace. It is estimated at US$43,000-54,000.

Padparadscha sapphire weighing 10.27 carats. It is estimated at US$80,000 - 86,000.

Cabochon emerald of 24.49 carats, est US$150,000-210,000.

Necklace composed of nine jadeite cabochons accented by pear and brilliant-cut diamonds. The suite has a pre-sale estimate of US$190,000-260,000

Emerald, Ruby and Diamond Necklace, Brooch and Earring Suite circa 1965. 27.20 carats of diamonds, approximately 36 carats of emeralds and approximately 105 carats of Burmese rubies. It has a pre-sale estimate of US$120,000-150,000