ry wheels, emery cloth, emery paper, etc., to see that the
material is tough. Any of the corundum gems therefore may be used in any
type of jewel without undue risk of wear or breakage. Customers of
jewelers should, however, be cautioned against wearing ruby or sapphire
rings on the same finger with a diamond ring in cases where it would be
possible for the two stones to rub against each other. So much harder
than the ruby is the diamond (in spite of the seeming closeness of
position in Mohs's scale) that the slightest touch upon a ruby surface
with a diamond will produce a pronounced scratch. The possessor of
diamonds and other stones should also be cautioned against keeping them
loose in the same jewel case or other container, as the shaking together
may result in the scratching of the softer materials. The Arabs are said
to have a legend to the effect that the diamond is an _angry_ stone and
that it should not be allowed to associate with other stones lest it
scratch them.

CHRYSOBERYL. Passing on to the next mineral in the scale of hardness we
come to chrysoberyl, which is rated as 8-1/2 on Mohs's scale. This
mineral furnishes us the gem, alexandrite, which is notable for its
power to change in color from green in daylight to red in artificial
light. Chrysoberyl also supplies the finest cat's-eyes (when the
material is of a sufficiently fibrous or tubular structure), and it
further supplies the greenish-yellow stones frequently (though
incorrectly) called "chrysolite" by jewelers. The material is very hard
and reasonably tough and may be used in almost any suitable mounting.

SPINEL. After chrysoberyl come the materials rated as about 8 in
hardness. First and hardest of these is spinel, then comes true or
precious topaz. The various spinels are very hard and tough stones. The
rough material persists in turbulent mountain streams where weaker
minerals are ground to powder, and when cut and polished, spinel will
wear well in any jewel. The author has long worn a ruby spinel in a ring
on the right hand and has done many things that have subjected it to
hard knocks, yet it is still intact, except for a spot that accidentally
came in contact with a fast-flying carborundum wheel, which of course
abraded the spinel.

TOPAZ. The true topaz is a bit softer than spinel, and the rough
crystals show a very perfect basal cleavage. That is, they will cleave
in a plane parallel to the bases of the usual orthorhombic crystals.
T