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Gem-Stones and Their Distinctive Characters

Chapter 121: TABLE III
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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 III

Refractive Indices of Gem-Stones[8]
Opal 1·454
Moonstone 1·53 1·54
Iolite 1·543 1·551
Quartz 1·544 1·553
Beryllonite 1·553 1·565
Beryl 1·578 1·585
Turquoise 1·61 1·65
Topaz 1·618 1·627
Andalusite 1·632 1·643
Tourmaline 1·626 1·651
Apatite 1·642 1·646
Phenakite 1·652 1·667
Euclase 1·651 1·670
Spodumene 1·660 1·675
Enstatite 1·665 1·674
Peridot 1·659 1·697
Axinite 1·674 1·684
Diopside 1·685 1·705
Idocrase 1·714 1·719
Spinel 1·726
Kyanite 1·72 1·73
Epidote 1·735 1·766
Garnet (Hessonite) 1·745
Chrysoberyl 1·746 1·753
Garnet (Pyrope) 1·755
Benitoite 1·757 1·804
Corundum 1·761 1·770
Garnet (Almandine) 1·790
Zircon (a) 1·815
Garnet (Demantoid) 1·885
Sphene 1·901 1·985
Zircon (b) 1·927 1·980
Diamond 2·417