Home » categories » rare book library » Castellani. Gems.
This chapter is tagged (labeled) with: 

ELECTRICITY

BRIGHTNESS, COLOUR, AND TRANSPARENCY. Page of 243 FUSION AND SOLUTION Text size:minus plus Restore normal size   Mail page  Print this page
INTRODUCTION.
9
Many crystals present beautiful changes of light, when this is reflected in certain given directions, as in the Labradors, the moon-stone, and the Asteria.
Minute crevices cause the iridescence, as in the stone called Iris.
Many gems are more or less transparent ; that is, they possess in a greater or less degree the power of transmitting light; and, according to these degrees, they have different denominations. That stone is called " transparent " which, when placed before an object, does not impede its view.
When the stone allows an object to be seen indis­tinctly through it, it is called " semi-transparent," and " translucent " when it allows the light to pass, but hinders the view of objects.
ELECTRICITY.
Electricity is produced in gems by heat, friction, or violence. In some gems it is caused by warming them at the fire, and then they are said to possess pyrelectri-eism. Electricity is produced by friction in the topaz, the amethyst, all quartz, the diamond, the garnet and emerald. Some crystals become electrical by percussion, as, for instance, the Iceland spar.
Some stones conduct, others reject electricity, which in those cases is either positive or negative.
The power of retaining electricity when produced is very variable in stones, and the time which elapses
BRIGHTNESS, COLOUR, AND TRANSPARENCY. Page of 243 FUSION AND SOLUTION
Suggested Illustrations
Other Chapters you may find useful
Other Books on this topic
bullet Tag
This Page