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Ruby RI 1.76–1.78
The best ruby material has
excellent brilliance, as well as its
striking red colouring.Jadeite RI 1.65–1.68
Jadete varies in colour, and is white
in its pure form. It has a moderate
amout of dispersion.Onyx RI 1.54–1.55
Onyx can be black or brown with
white colour banding, giving a fairly
restrained dispersion.Sodalite RI 1.48
Transparent sodalite is rare, and its
RI is low; however, good-quality
gemstones can be cut.Chrysocolla RI 1.46–1.57
Chrysocolla is generally
blue-green and massive. Its
fire and brilliance are
moderately low.Spessartine garnet
RI 1.79–1.81
Gem-quality spessartine
crystals are rare, but
have good dispersion.Opal RI 1.37–1.52
Opal has a distinctive colour play,
which comes from diffraction
caused by tiny silica spheres.Fluorite RI 1.43
With one of the widest
colour ranges of any
mineral, fluorite has
moderate brilliance.Obsidian RI 1.45–1.55
Despite its deep black
colouring, obsidian is more
refractive than some gems.FIRE AND BRILLIANCE
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