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PRECIOUS STONES
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refraction. For difference between spinel and essonite, refer to No. 5.
21. Brownish-Yellow Varieties of Topaz, Citrine (same
as Cairngorm only Yellow Tints), Epidote, Vesuvianite, Axinite, and Sphene
Remarks
in No. 19 will apply to these. In addition, topaz is more deeply yellow
in coloring, and harder than the others. Sphene is almost as soft as
glass, does not give such decided colors under the dichroiscope, shows
generally a greenish tendency, and is rarely quite transparent.
22. Hyacinth, Yellow Sapphire, Chrysoberyl, Chrysolite,
Topaz, Golden Beryl, and Citrine (in Yellow)
Of these, the sapphire, topaz, beryl, and citrine are at times most nearly alike in general appearance.
The
sapphire has a harder lustre and is generally like the light-yellow
topaz. They are both more transparent than citrine, and usually lack
the rich depth of the beryl's yellow. The hyacinth is distinguished by
an inclination to red (it is never clean yellow) which does not appear
in any of the others except topaz. Chrysoberyl and chrysolite have a
similar tendency towards green. They are all double refraction stones,
but the twin colors are decided only in the topaz (light and dark
yellow). The variations of hardness and specific gravity between those
most alike are sufficient to separate them with ease. The fluorite, a
single refraction stone, softer than glass, is yellow also, but cannot
be mistaken for either of the others.
Hardness. Specific Gravity.
Yellow sapphire.........................9 3.9 to 4.1
Chrysoberyl................!............8.5 3.68 to 3.78
Topaz..................................8 3.50 to 3.56
Hyacinth................................7.5 4.6 to 4.7
Citrine..................................7 2.65
Chrysolite...............................6.5 3-33 to 3-37
Fluorite.................................4 3.1
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