While
the ruby holds its own by candle and gas light, the sapphire generally
becomes dull, often acquiring a somewhat purplish or amethystine hue.
The white sapphire of modern writers is, in all probability, included under the adamas of Pliny ; the blue sapphire is the ancient hyacinthus ; while the true ruby, the spinel, and certain red garnets were the several varieties of Pliny's carbuncidus, under which name the writer included several stones which were perfectly distinct from one another.
In
concluding this account of the transparent varieties of corundum
mention may be made of the extreme ingenuity with which, in a pale or
poor coloured sapphire, the native lapidary in Ceylon will take
advantage of the presence of a streak or spot of rich colour. He will
so cut the stone as to throw this colour into the entire gem.
Spinel.
No
precious stone includes so wide a range of colours as the spinel.
Following the order of the rainbow, we have red, orange, green, blue,
and violet-coloured spinels ; and also those which show the hues known
as purple, puce, and indigo. Yellow spinels are not unknown ; some are
colourless, others black. Another character of importance which
enchances the position of the spinel as a gem stone is its hardness,
which, though inferior to that of the rubv. is greater than that of the
red garnet. But over against these excellences of the spinel must be
set the lack of fire, due to its small refractive and dispersive power
; and also the somewhat prosaic qualitv of its colour, attributable in
part to the absence of pleochroism. It is perhaps unfortunate for the
appreciation of this species of precious stone that its red varieties
seem to enter into competition with the incomparable splendour of the ruby, and its blue varieties with the velvety softness of the sapphire. 844.5.
K 2
