The color in zircon (ZrSiO4) comes from both
uranium ions and radiation damage. U4+ enters the zircon
because, like Zr4+, it has a large ionic radius. U4+
substituting in zircon causes the blue color of heat-treated zircon.
geologic time, the uranium undergoes radioactive decay and the
radiation damage centers cause a range of red-brown and amber colors.
treatment removes the radiation damage centers and restores the blue
color with which zircon presumably originally crystallized. Green
are associated with a mixture of the blue color from uranium and
color from radiation damage centers. Highly radiation-damaged zircons
called metamict zircons. Colorless zircons have little uranium.
Zircon Visible Spectra (400 - 1200 nm)
- Zircon 1844 ;
from Chanthaburi, Thailand, colored by radiation damage. Data files: a
(24K) ; c (24K)
- Zircon 1486 ;
partially metamict zircon from Sri Lanka colored by radiation damage.
lines from U4+ are seen in the spectrum of the 4.4 mm thick
sample. Data files: a (24K)
- Zircon 1898; Blue zircon from Burma, near
the Thailand border. This 2.65 mm thick crystal may have been
to remove a brownish-red initial color. Data files: a
(20K); c (20K)
- Zircon; medium green
from Burma(?). This 6 mm thick crystal has moderately intense alpha
activity. Data files: unpolarized
- A pale brown, a green and a red zircon from Mogok, Myanmar:
- Zircon 340, a deep orange-brown metamict
zircon from Sri Lanka. The spectrum of this 1.044 mm thick, highly
radioactive crystal does not change with polarization direction. When
thick , its color is black. Also called zircon 6500 (for 6500 ppm equivalent uranium) and zircon #83057. Extended range spectrum showing OH absorption. Data file: unpolarized
- Thorite; Green thorite compared to
Both of these show an uranium spectrum.
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