Wednesday, 28 July 2021

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 discovered in 1886 and became a favorite of Russian royalty and designer Carl Fabergé.
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 brilliance to two 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  highly coveted.
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.

Tuesday, 27 July 2021

Spinel of Mahenge, Tanzania

Spinel is magnesium aluminum oxide with the formula MgAl2O4. The name "spinel" comes from either the Latin word "spina" meaning "thorn", due to its characteristic octahedral crystals having pointed ends, or the Greek word "spintharis" meaning "spark".

Although spinel occurs in a range of different colors, the pink to red variety is the one that is commercially important. Spinel is single refractive and doesn't have pleochroism. It belongs to the cubic crystal system with hardness of 8.0 on the Mohs scale.
Spinel offers a range of hues from orange to intense red, vibrant pink, and all shades between purple, blue and violet through to bluish green.
Historically, the most famous red spinels came from the Balas region of Afghanistan and were known as Balas rubies. Some of the most famous rubies in the world, such as the Black Prince's Ruby, part of the British Crown Jewels, are actually spinels. More recently, Sri Lanka and Burma has been the main source for fine spinel.

The highest quality transparent blood-red "ruby spinel" and hot-pink spinel has come from mines in Mogok, Upper Burma.
In 2007 several huge spinel crystals were discovered at Ipanko, near the town of Mahenge, in Tanzania. Miners unearthed spinel crystals weighing from six to 54 kg.
The crystal was highly included, but large chunks of top quality stone were able to be cobbed off.
The spinel crystal displayed the vibrant pink color that is now famous from Mahenge Spinel. Thousands of carats of gem quality gems were cut in Thailand and distributed into the world market.

From this point on Mahenge Spinel was thrust into the world spotlight.
Spinel is highly sought after by gem connoisseurs, and well-formed spinel crystals are in high demand among collectors. Red spinel range from orange-red to purplish red, with pure red considered the finest of all.

A top-quality 5 carat red spinel might sell for around a tenth the price of an equivalent-quality ruby, and pink spinel often sells for less than pink sapphire.
Tanzania is now the world's second largest supplier of spinel in the pink-to-red range. Spinel also has been found in Ipanko and Matombo.

Since the Mahenge spinel is still a recent discovery, there is still top quality material available for collectors.

Weathered marble outcrops tower over the spinel diggings of Ipanko, near Mahenge.
The Imperial Crown of Russia, also known as the Great Imperial Crown, was made for the Empress Catherine II the Great's Coronation in 1762. The crown is set with around 5000 diamonds from India arranged in a pattern of laurel wreaths and oak branches and a number of fine large white pearls.

It is topped with one of the seven historic stones of the Russia's Diamond Collection - a large precious red spinel weighing 398.72 carats. The Imperial Crown of Russia is currently on display in the Moscow Kremlin Armoury State Diamond Fund.
The Imperial State Crown is the most magnificent of all the Crown Regalia. It was made in 1838 for the Coronation of Queen Victoria, and then altered for the Coronation of George VI in 1937 and Elizabeth II in 1953. It is usually worn at the end of the coronation ceremony, when the newly-crowned monarch departs from Westminster Abbey. Although the crown is modern in design, it is set with very old gems.

The Black Prince’s Ruby (spinel), roughly 170 carats, is set into the central panel of the crown.

Saturday, 24 July 2021


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 significantly.

Saturday, 17 July 2021

Bvlgari - Magnifica 2021

The Bvlgari Magnifica Imperial Spinel necklace boasts a center 131.21 carat spinel, the world's 4th largest.
The latest Bvlgari collection consists of 350 masterpieces, 122 of which have never been seen before.

Thursday, 15 July 2021

Ruby shines in high collections

David Morris. Rubia cabachon choker with 380 carats of Burmese Ruby.
Cartier. Phaan ring.

Van Cleef & Arpels’ Sous les Etoiles collection.

Bvlgari Ruby Metamorphosis necklace. 10.02-carat Mozambique ruby.
Albertine Ballerina clip by Van Cleef & Arpels

Valani Atelier x Gemfields Vela Earrings