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XXV
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DISTINCTIVE CHARACTERISTICS OF VARIOUS
STONES
There are
some marked characteristics of certain stones which it is well to
remember. Spinel and the garnets, like the diamond, are singly
refractive.
Light reflected from the spinel is always yellow.
The lustre of the zircon, like that of the diamond, is adamantine.
Garnet, topaz, and tourmaline become electric by heating, as well as by friction.
Heat changes the color of topaz; it also changes the color of spinel and ruby, but the color returns as it cools.
Diamond, rock crystal, zircon, and fluorite are phosphorescent.
The green of the tourmaline tends towards blue; of the chrysolite and chrysoberyl, to yellow.
The red of the ruby inclines to blue or purple; of spinel, to yellow; of garnet, to both purple and yellow.
The blue of the sapphire has a purplish tendency; of the tourmaline, a greenish.
Mixed colors appear in the andalusite, sphene, and some brown tourmalines.
Imitations
are warmer to the touch than stones, and a drop of water flattens and
spreads over the surface as it does not on the genuine. An aluminum
point will leave a mark upon the surface of an imitation when drawn
over it. It will not do so on the precious stones.
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