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Gem-Stones and Their Distinctive Characters

Chapter 123: TABLE V
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About This Book

A practical handbook describing the physical characters and identification methods for gemstones, combining clear accounts of crystalline form, optical properties (reflection, refraction, dispersion, double refraction), colour and absorption effects, specific gravity, hardness and electrical behaviour with practical techniques such as refractometer use and heavy-liquid tests. It outlines cutting, weighting and nomenclature, distinguishes manufactured and imitation stones, and provides species-by-species descriptions of precious and semi-precious gems — including diamond, corundum, beryl, topaz, spinel, garnet, tourmaline, zircon, quartz and chrysoberyl — accompanied by diagrams, plates and tables of physical constants for practical reference.

TABLE V

Character of the Refraction of Gem-Stones
(a) Single
Diamond, spinel, garnet, opal.
Diamond and garnet frequently display local double refraction.
 
(b) Uniaxial, Positive
Quartz ·009
Phenakite ·015
Benitoite ·047
Zircon (b) ·053
Quartz exhibits circular polarization.
 
(c) Uniaxial, Negative
Apatite ·004
Idocrase ·005
Beryl ·007
Corundum ·009
Tourmaline ·025
 
(d) Biaxial, Positive
Chrysoberyl ·007
Topaz ·009
Enstatite ·009
Spodumene ·015
Euclase ·019
Diopside ·020
Peridot ·038
Sphene ·084
 
(e) Biaxial, Negative
Moonstone ·006
Iolite ·008
Axinite ·010
Andalusite ·011
Beryllonite ·012
Kyanite ·016
Epidote ·031