Home » categories » rare book library » Wodiska. A Book of Precious Stones.

Ch. 20: Tourmaline

Ch. 20: Tourmaline Page of 451 Ch. 20: Tourmaline Text size:minus plus Restore normal size   Mail page  Print this page
162 A Book of Precious Stones
columnar and black, without cleavage or trace of fibrous texture.
Tourmaline heated, like some other minerals in which one termination differs in form from the other, develops electricity, with the effect of making of the ends positive and negative poles. Sections of tourmaline crystals cut parallel to the axis have the property of polarising light. Tourmaline can be fused under the blowpipe to a spongy enamel; it melts with borax to trans­parent glass. Tourmaline is cut step and bril­liant.
Twin-coloured tourmaline is strongly doubly refractive; green shows yellow and greenish blue; yellowish green, yellow and green; red­dish brown, light and dark brown; red, pink and dark red; blue, light and dark blue. The green tends toward blue while the blue has a greenish tendency. Some brown tourmalines have mixed colours.
In considering shades when selecting tourma­lines, a medium bright green is better than the lighter or that which appears blackish. The pink should be deep and clean, ruby-like. A rich amber brown is most desirable of the brown shades. Red tourmaline is occasionally so like the ruby that it might deceive any but the ex-
Ch. 20: Tourmaline Page of 451 Ch. 20: Tourmaline
Suggested Illustrations
Other Chapters you may find useful
Other Books on this topic
bullet Tag
This Page