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PRECIOUS STONES
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monds
in betrothal rings. Pretty as is this conceit, there is no doubt about
the fact that the gift of diamonds to the object of one's affections
does usually produce a feeling of pleasure to both parties, from which
it would appear that there is some ground for the belief.
Corundum.
This mineral is a species of crystal, or crystalline alumina—an almost pure anhydrous alumina, A1203—in
many varieties, both of shape and colour. The chief stone is the ruby,
considered, when large, to be of even more importance and value than
the diamond. There are many other red stones in this group : sapphires,
also, are a species of corundum, both the blue and the colourless
varieties, as are also the aquamarine, the emerald, the amethyst, the
topaz, and others, all of widely differing colour, as well as the
star-shaped, or " aster " ruby, called the " ruby " cat's-eye. All
these vary more in colour than in their chemical properties. Still
another variety, greyish-black and generally associated with haematite
iron ore, is called emery, and, when ground in different degrees of
fineness, is so well known by its general use as a polishing medium as
to need no description. It should, however, be mentioned that amongst
the more coarsely ground emery it is no uncommon thing to find minute
sapphires, taking sapphires in their broad, commercial meaning, as
signifying any variety of corundum, except the red and the emery. The
surfaces of crystals of corundum are often clouded or dull, whilst its
classification of lustre is vitreous. It is double refracting and
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