at
Matura, Ceylon. Colourless or smoky zircons are called jargons or
jargoons. Transparent zircons of a brownish, red-orange colour are
called hyacinth or jacinth. Zircon is the heaviest gem mineral—more
than four times the weight of water—its specific gravity being 4.2 to
4.86. Its hardness is 7-1/2 So high is its index of
refraction—1.92—that it approaches the diamond in brilliancy when cut.
Zircons of gem quality come mostly from Ceylon, where they are found in
the form of rolled pebbles. Zircon is found in various American
localities, but it is opaque.
