displacement
of five carats, and the result, 3, would be the specific gravity of the
stone. Thus, absolute weight, fifteen carats; specific weight, ten
carats; loss, five carats: 15 -5-5 = 3, specific gravity.
All
minerals are electric. Some acquire electricity by heating, some by
friction, others by either method. Some display positive, and others
negative, electricity. Although the diamond is a non-conductor, it
becomes positively electric by friction, and it differs from other
stones in that it is electric in the rough also. And the different
stones vary in their power to retain electricity: some can do so for a
few minutes only; others for many hours.
Those minerals which become electric by heating are said to be pyro-electric, from the Greek nop, fire,
and electric. The tourmaline, when heated, shows positive electricity
at one end of the prism, and negative at the other. The other
hemihedrally modified prisms (topaz, for instance) have the same
peculiarity.
The
chrysolite and several forms of garnet possess the power to act on the
magnetic needle. The tourmaline and others, after friction, will
attract and hold small bits of paper and the like; and the Brazilian
topaz, made electric by friction or heating, will affect the electric
needle after many hours.
Many
precious stones become distinctly phosphorescent by exposure to
sunlight, or by the application of heat, or other electrical and
mechanical methods. This is true of the diamond, rock crystal, ruby,
zircon, and fluorite. Some diamonds are much more phosphorescent than
others. There are diamonds which assume a deep violet hue under the arc
light. Upon experimenting with stones of this character, Mr. George F.
Kunz found that they displayed phosphorescence to an unusual degree,
possessing the quality of storing up sunlight and electric light, and
emitting the same in the dark. He also observes that these stones are
generally slightly
