Have you heard of Zimmi Yellow diamond? If so, do you know what makes Zimmi Yellow diamond unique amongst the other normal yellow diamond? This article will explain the differences between a Zimmi Yellow diamond and a Normal diamond. Zimmi Diamond is a rare Vivid Yellow diamond from the Zimmi region. Zimmi diamond is originated from the name of the Mine in Sierra Leone, known as Zimmi mine where the deepest natural yellow diamonds are found. There are various types of yellow diamonds which are known as Canary diamond, Cape diamond and Zimmi Yellow diamond . These diamonds are much likely to be influenced by the carbon atom in the lattice, making them different in their colour intensity and saturation. Zimmi yellow diamond is rare, with only one out of approximately 10,000 carats mined is a Natural Fancy colour diamond.
Image Courtesy: Leibish
From the left a 5.91 carats Zimmi Vivid Yellow diamond ring and a 1.25 carats Fancy Vivid Yellow diamond ring.
Image Courtesy: Robert Weldon
Two Bright Zimmi diamonds weigh 1.03 and 1.02 carats from an alluvial deposit in the Zimmi mining area in Southern Sierra Leone (James Shirley, Christopher M 2002-2021)
Types of diamond
Did you know that the colour of the diamond is mainly influenced by the structure of the chemical bonds? these chemical bonds are usually made up of nitrogen and boron atoms. The yellow colouration in a diamond is caused by tiny amounts of nitrogen impurities in the carbon lattice. In total, there are 2 types of diamonds chemical bond. The first type is categorised as laA and IaB which contain mostly nitrogen cluster. It is known that 95% of natural diamonds are made up of laA type, which is in the category of near colourless to yellow. Most of the laA diamonds come from Cape Province, South Africa. They are known as Cape diamond. Type lb diamonds contain isolated nitrogen atom instead of being in a cluster. They are usually known as the Canary yellow diamond, which is also perceived as the Zimmi Yellow diamond. The second type is categorised as lla and llb which does not have any presence of nitrogen impurities. Type lla is usually colourless but can be light brown, light yellow or light pink. Type llb diamonds are normally blue or grey, and these diamonds conduct electricity because of Boron impurities in their lattice structure.
Image Courtesy: GIA
Image Courtesy: GIA
The historic Wittelsbach Blue diamond known as type llb diamond that
conducts electricity and known for its blue colour
Zimmi Yellow diamond MINE
Zimmi Mine refers to a small town in the Pujehun district of Sierra Leone. The mining area produces some of the world's Fancy Intense Yellow and Fancy Vivid Yellow diamond known as the Zimmi Yellow Diamond. The diamonds are usually highly saturated in colour and weigh between 0.10 and over 1.00 Carat weight. The weight of the rough diamonds can be found up to 4 carats. Rough diamonds from the Zimmi mine are usually smooth and rounded dodecahedral. This makes the Zimmi Yellow diamond more suitable for cutting. Since it's perceived as rare and high saturation in yellow colour, a Zimmi Yellow diamond is priced higher than normal diamond.
Image Courtesy: Zimmimine Image Courtesy: Google
Operation of Zimmi Yellow Diamond mine
In September 2018, Sierra Leone's Government came out with a journal about mining. One of the pages highlighted Sierra Leone's mining industry new direction. They are welcoming investors to invest in Sierra Leone's mine at the same time, ensuring that their people get maximum benefits from the mineral wealth. As research has shown that Zimmi Yellow diamonds are still sold in auctions house like Sotheby, Christie and some fine jewellery Company website, thus this shows that the operations of the Zimmi Yellow diamond mines are still operating despite it being rare.
Image Courtesy: mining-journal
6.70 Carats of Natural Fancy Deep Yellow Zimmi Diamond with VS1 clarity estimated price at US $450 000 705,000
Image Courtesy: A Magazine
Normal Diamond VS Zimmi Yellow Diamond
The oriental Sunrise earring from Christie's website is estimated to cost about US $12 million. The white diamond and gold on both earrings are estimated to cost US $180 thousand. After subtracting the white diamond and gold on a pair of earrings, the Zimmi Yellow gemstone itself is estimated to cost around $11.4 million per pair. Which is about US $470 000 per carat. Each Fancy Vivid Orange-Yellow oval-cut diamond weighs approximately 12.20 and 11.96 carats. Meanwhile, the Sun-Drop Pear-Shaped diamond Diamond Vivid Yellow diamond was sold approximately at $12 million US dollars. The Pear-Shaped Yellow diamond cut itself weighs approximately 110 carats. This means it was sold at an estimation of $11 000 per carat. In comparison, the price of the Oriental Sunrise Zimmi Yellow diamond's earrings is much more expensive than the Sun-Drop pear-shaped diamond because of its differences in colour and saturation.
Image Courtesy: Christie Image Courtesy: Sotheby
Just last year in November 2020, a 28.88 Carat Fancy Vivid Yellow diamond is priced at an estimation of US $3.1 million. The rectangular step-cut diamond has a VV2 clarity. After calculating, the diamond was sold at an estimation price of US $107 600 per carat. Comparing the price of the Fancy Vivid Yellow diamond and the Oriental Sunrise Zimmi Yellow diamond's earrings, The Zimmi Yellow diamond cost 4 times more than the Fancy Vivid Yellow diamond.
Image Courtesy: Christies
Meanwhile, the Bague Fancy light yellow cushion-cut Fancy Light diamond weighing 1.50 carats is sold at an estimated price of US$4500. On the left, a Cartier Fancy Intense Yellow Diamond ring that weighs 5.24 carats is priced at an estimation of US $75 000-$100,000.
Image Courtesy: Sothebys
Defects in Zimmi diamond Vs Normal Yellow diamond
Defects in diamonds are the one that causes diamonds to be yellow or either orange in colour. The cape defects are high in nitrogen and dispersed defect, hence the diamond produces a pale yellow colour. The isolated nitrogen has a single carbon atom which Zimmi Yellow diamond falls into this category hence it produces a deeper to intense yellow canary to brown colour. The graph of the isolated nitrogen shows from an increase to decrease and the further it bends, the more the colour of the diamond will turn into deep orange. The 480 NM band is an unknown structure as a result, it produces a pale orange colour which can be perceived as an attractive colour too. Last, the H3 band produces a yellow and green overtone as the structure has a pair of a nitrogen atom in an empty spot. This shows how nitrogen impurities play an important role in determining the colour and saturation of a diamond.
Image Courtesy: GIA
Image Courtesy: naturallycoloured
Inclusion in Zimmi Diamond Vs Normal diamond
Zimmi Yellow diamond is in the isolated nitrogen lb category because of the occurrence of the single-atom it produces Fancy Intense and Fany vivid yellow diamonds. The inclusions in the yellow diamond are like a white oriented needle. While Cape defects have big patterned clouds inside inclusions. While for the 480 NM, it band has disc-shaped inclusion and tiny particle. It is quite fascinating to see how these inclusion in a different type of diamonds are different in size, orientation and shapes. As shown on the picture on the left, the picture of Zimmi Yellow diamond which has metallic sulfide mineral inclusions, surrounded by a black graphitised feather inside. (James Shigley, Christopher M 2002-2021)
Image Courtesy: GIA Image Courtesy: GIA
Type Ib diamonds like Zimmi Yellow diamonds are rare and attractive because with time and heat, isolated nitrogen impurities in the lattice cluster, will cause complicated defects like IaA and IaB diamonds type. Also, since diamonds usually spend their time in the lower crust and upper mantle of the earth, it is rare for isolated nitrogen in the Ib type of diamond to not go through the process of clustering which will cause complicated defects. According to GIA, this mystery makes the discovery of Zimmi Yellow diamonds in Sierra Leone more interesting and unique.