JARGOON, or

See also:

• JARGON

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 t y 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 .