variation occurs in the specific gravity, namely, from 3·3 to 3·5. [Illustration: _PLATE XXVII_ 1. RUBELLITE 2. TOURMALINE 3. BALAS-RUBY 4. BLUE SPINEL 5. QUARTZ 6. WHITE OPAL 7. AMETHYST 8. TOURMALINE 9. BLACK OPAL 10. FIRE OPAL 11. ALEXANDRITE (_By daylight_) 12. CHRYSOBERYL 13. ALEXANDRITE (_By artificial light_) GEM-STONES] Peridots of deep bottle-green hue command moderate prices at the present day, about 30s. a carat being asked for large stones; the paler tinted stones run down to a few shillings a carat. The rate per carat may be very much larger for stones of exceptional size and quality. Olivine, to use the ordinary mineralogical term, is a common and important constituent of certain kinds of igneous rocks, and it is also found in those strange bodies, meteorites, which come to us from outer cosmical space. Except in basaltic lavas, it occurs in grains and rarely in well-shaped crystals. Stones that are large and transparent enough for cutting purposes come almost entirely from the island Zebirget or St. John situated on the west coast of the Red Sea, opposite to the port of Berenice. This island belongs to the Khedive of Egypt, and is at present leased to a French syndicate. It is believed to be the same as the mysterious island which produced the ‘topaz’ of Pliny’s time. Magnificent stones have been discovered here, rich green in colour, and 20 to 30, and occasionally as much as 80, carats in weight when cut; a rough mass attained to the large weight of 190 carats. Pretty, light-green stones are supplied by Queensland, and peridots of a less pleasing dark-yellowish shade of green, and without any sign of crystal form, have during recent years come from North America. Stones rather similar to those from Queensland have latterly been found in the Bernardino Valley in Upper Burma, not far from the ruby mines. CHAPTER XXVI ZIRCON (_Jargoon_, _Hyacinth_, _Jacinth_) Zircon, which, if known at all in jewellery, is called by its variety names, jargoon and hyacinth or jacinth, is a species that deserves greater recognition than it receives. The colourless stones rival even diamond in splendour of brilliance and display of ‘fire’; the leaf-green stones (Plate XXIX, Fig. 13) possess a restful beauty that commends itself; the deep-red stones (Plate XXIX, Fig. 14), if somewhat sombre, have a certain grandeur; and no other species produces such magnificent stones of golden-yellow hue (Plate XXIX, Fig. 12). Zircon is well known in Ceylon, which supplies the world with the finest specimens, and is highly appreciated by the inhabitants of that sunny isle, but it scarcely finds a place in jewellery elsewhere. The colourless stones are cut as brilliants, but brilliant-cut fronts with step-cut backs is the usual style adopted for the coloured stones.