ones--particularly those from South Africa
and Brazil--are tinted when uncut, probably by reason of the action upon
them of their matrix, especially if ironstone, or with rolling for ages
amongst ironstone in river-beds, which gives them a slight metallic
appearance; in each case the cause is suggested by the fact that these
tinted stones are usually found in such places, and that the tinting is
very thin and on the surface only, so that the cutting and shaping of
the stone gets below it to the perfectly clear diamond.

From Pliny and other historians we gather that at various periods
considerable superstition has existed with regard to diamonds, such as
that if one is powdered it becomes poisonous to a remarkable degree;
that gifts of diamonds between lovers--married and unmarried--produce
and seal affection; hence the popularity of diamonds 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, Al_{2}O_{3}--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 has no cleavage. It is found in China, Ind