Jargoon

A Jargoon or jargon (occasionally in old writings jargounce and jacounce) is name applied by gemologists to those zircons which are fine enough to be cut as gemstones, but are not of the red color which characterizes the "hyacinth" or jacinth. The word is related to Arab "zargun" (zircon). Some of the finest jargoons are green, others brown and yellow, whilst some are colorless. The colorless jargoon may be obtained by heating certain colored stones. When zircon is heated it sometimes changes in color, or altogether loses it, and at the same time usually increases in density and brilliancy. The so-called "Matura" diamonds, formerly sent from Matara (or Matura) , in Sri Lanka, were decolorized zircons. The zircon has strong refractive power, and its lustre is almost adamantine, but it lacks the fire of the diamond. The specific gravity of zircon is subject to considerable variation in different varieties; thus Sir A. H. Church found the specific gravity of a fine leaf-green jargoon to be as low as 3.982, and that of a pure white jargoon as high as 4.705. Jargoon and tourmaline, when cut as gems, are sometimes mistaken for each other, but the specific gravity is distinctive, since that of tourmaline is only 3.103. Moreover, in tourmaline the dichroism is strongly marked, whereas in jargoon it is remarkably feeble. The refractive indices of jargoon are much higher than those of tourmaline.

References

* [http://www.farlang.com/gemstones/kunz_gems_and_precious_stones/page_120 Kunz: Gems and Precious stones of North America; Zircon]