By this name, which comes from the appellative of rubeus, on
account of their colour, three gems are known, very different in their
constitution, but resembling each other in colour so as often to be
confounded together ; they are the red ' corundum or Oriental ruby,
the red spinel, and the balais. We shall treat of them separately.
1. ORIENTAL RUBY.
The gem most prized next to the diamond is the ruby, or red corundum of the naturalists.
splendour of its tints, sometimes purely red, at other times violet,
pink, or purple, makes it the most beautiful coloured gem in nature.
hardness of the Oriental ruby is immediately second to that of the
diamond, and it is superior to that of the other corundums.
has double refraction, although not of a high degree ; its light is
vitreous ; it bears the strongest fire without losing colour or form,
but by means of a special solvent it is transformed with difficulty
into a clear glass.
is easily perceived from its crystals that it has experienced the
action of fire, but, notwithstanding, they are capable of cleavage.
Their form is not well defined, generally oval and imperfect, but still
octagonal or round, or flattened at one part.