or
by Zircon whose colour has been discharged by heating. Diamond differs
from all these by its greater dispersive power and consequent greater "
fire." Its lustre is much higher than that of any of the other minerals
mentioned, except Zircon, which may approach it. Probably the most
ready test of all is that of hardness, and for this purpose carborundum
is very well suited, for should the stone be genuine, it will not be
scratched, but should an inferior stone have been fraudulently
substituted the carborundum will scratch it, even if it be of hardness
equal to 9 of Mohs' scale (Corundum). It should be noticed that both
the crown and the culasse should be tested (see " Doublets " under
Artificial Production). In considering the purchase of a valuable stone
it should always be seen unmounted. Its single refraction would show it
to be a cubic mineral, while of the above imitations only Spinel agrees
in this respect, and Spinel is readily distinguished by its inferior
hardness. The specific gravity of Diamond also is of some help, though
Spinel, Topaz and possibly Tourmaline might be confused with it in this
respect.
Glass
imitations have almost as high a dispersive power, if good, but their
inferior hardness is very marked, and good glass imitations are usually
sold as such.
The
great test in De Boot's time was that of applying the " tincture "—the
varnish mentioned above; a Diamond became more brilliant, but an
imitation became less brilliant when the "tincture" was applied to the
under surface.
Famous Diamonds.
A Diamond whose history is as old as any, perhaps, was the one worn by Charles the Bold in his pendant, It was
