231. CORUNDUM.
This mineral
species includes some of the most important precious stones, its blue
crystalline variety being the Sapphire and the red the Ruby, while
other colours are known as Oriental Topaz, Oriental Amethyst, etc.
Since these are all the same mineral, with only slight variations in
the colouring matter, they will all be treated collectively so far as
possible. To the old writers they were regarded as of many species.
Thus the Sapphire was the Hyacinth us of Pliny, and included his
variety Asteria. The Ruby was regarded by him as belonging to the
Lychnis group of the Carbunculi; but much confusion of terms has crept
in in the writings of many of the early mineralogists.
Dependent
on the colour is the jeweller's classification of the varieties ;
mineralogically these are sub-varieties of the crystallised Corundum.
The two most common kinds are the blue Sapphire and the red Ruby; but,
as indicated above, a number of other colours occur which are
practically identical with the colours of other well-known gems, and
hence to distinguish the more valuable forms of Corundum the jeweller
prefixes the term " Oriental " to the name of the gem whose colour is
that of the stone in question. Thus Topaz is the mineral known to the
mineralogist by that name ; but Oriental Topaz is a yellow Corundum,
and the opposite term " Occidental" would be applied to such a
