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Wednesday, 19 September 2007

fezel (faizel). White streamer-like feathers ("intergrowths" on the twin plane) especially seen in a stone cut from a made.

Fiery Astrolite. Trade name for man-made lithium metaniobate.

fifth. A common abbreviation for a fifth carat.

fifty-nine-twenty line. A sharp ab­sorption line seen in the spectrum of most yellow and brown Diamonds in which the color has been imparted artificially by neutron bombardment and subsequent heat treatment. The application of this line (5920 A) to the detection of such diamonds was first described by Robert Crown-ingshield in Gems & Cemology, Vol. IX, No. 4. See absorption spec­trum.

Fifty Years of Aeroflot diamond. Named in commemoration of Soviet Aviation Day, this diamond, weigh­ing 232 carats, was found in the dia­mond field of Mirnyy in the Yakut-skaya region of Siberia. Discov­ered in August, 1973, it became the largest known Soviet diamond. Within three months, however, another diamond of identical weight, The Star of Yakutiya, was reportedly found in the same area.

file test. A test that is used princi­pally to separate glass imitations from diamonds, since a jeweler's file (hardness about 6V2) will scratch glass but not diamond. However, many natural and artificial stones that might be confused with dia­mond are harder than a file and thus cannot be separated from diamond by such a test. In addition, the thin edges of a diamond may be damaged by the test.

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