Jargoon

Jargoon, or Jargon (occasionally in old writings jargounce and jacounce), a name applied by modern mineralogists to those zircons which are fine enough to be cut as gem-stones, but are not of the red colour 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 colourless. The colourless jargoon may be obtained by heating certain coloured stones. When zircon is heated it sometimes changes in colour, 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 Ceylon, 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 sp. gr. 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 sp. gr. is distinctive, since that of tourmaline is only 3 to 3.2. 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 (see Zircon).

(F. W. R.*)