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A coloured diamond and diamond pendent necklace. Photo Christie's Image Ltd 2013

The rectangular-shaped fancy intense blue diamond weighing 0.56 carat, suspending a pear-shaped diamond weighing 3.06 carats, within a brilliant-cut diamond frame, spaced by a brilliant-cut diamond, joined to a collet-set brilliant-cut diamond fine neckchain, mounted in 18k white gold, 40.8 cm long. Price Realized $267,933

ACCOMPANIED BY REPORT NO. 2145621223 DATED 11 JUNE 2012 FROM THE GEMOLOGICAL INSTITUTE OF AMERICA STATING THAT THE 0.56 CARAT DIAMOND IS FANCY INTENSE BLUE, NATURAL COLOUR, INTERNALLY FLAWLESS CLARITY; ALSO ACCOMPANIED BY A SUPPLEMENTAL LETTER FROM THE GEMOLOGICAL INSTITUTE OF AMERICA STATING THE 0.56 CARAT DIAMOND HAS BEEN DETERMINED TO BE TYPE IIB. TYPE IIB DIAMONDS ARE VERY RARE IN NATURE (FROM OUR EXPERIENCE, LESS THAN ONE HALF OF ONE PERCENT) AND CONTAIN SMALL AMOUNTS OF BORON THAT CAN GIVE RISE TO A BLUE OR GREY COLORATION. AN UNUSUAL PROPERTY OF TYPE IIB DIAMONDS IS THAT THEY ARE SEMI-CONDUCTORS AND CONDUCT ELECTRICITY. HISTORICALLY, THE ANCIENT MINES OF INDIA PRODUCED OCCASIONAL BLUE DIAMONDS BUT TODAY THE MOST SIGNIFICANT SOURCE IS LIMITED TO THE CULLINAN (FORMERLY PREMIER) MINE IN SOUTH AFRICA. AMONG FAMOUS GEM DIAMONDS, THE 70.21 CARAT IDOL'S EYE AND THE 45.52 HOPE ARE EXAMPLES OF TYPE IIB

REPORT NO. 6142693593 DATED 6 MARCH 2013 FROM THE GEMOLOGICAL INSTITUTE OF AMERICA STATING THAT THE 3.06 CARAT DIAMOND IS D COLOUR, INTERNALLY FLAWLESS CLARITY, WITH EXCELLENT POLISH; ALSO ACCOMPANIED BY A SUPPLEMENTAL LETTER FROM THE GEMOLOGICAL INSTITUTE OF AMERICA STATING THE 3.06 CARAT DIAMOND HAS BEEN DETERMINED TO BE TYPE IIA. TYPE IIA DIAMONDS ARE THE MOST CHEMICALLY PURE TYPE OF DIAMOND AND OFTEN HAVE EXCEPTIONAL OPTICAL TRANSPARENCY. TYPE IIA DIAMONDS WERE FIRST IDENTIFIED AS ORIGINATING FROM INDIA (PARTICULARLY FROM THE GOLCONDA REGION) BUT HAVE SINCE BEEN RECOVERED IN ALL MAJOR DIAMOND-PRODUCING REGIONS OF THE WORLD. AMONG FAMOUS GEM DIAMONDS, THE 530.20 CARAT CULLINAN AND THE 105.60 CARAT KOH-I-NOOR, ARE EXAMPLES OF TYPE IIA 

Christie's . HONG KONG MAGNIFICENT JEWELS.28 May 2013. Convention Hall - http://www.christies.com