|
The crystal is full of cracks and fractures
due to metamictisation. Zircon is practically always 'doped'
with some thorium and/or other radioactive elements. The decay
of these atoms generates highly energetic, ionizing radiation
that is capable of destroying the structure of the crystal in
their vicinity. Therefore zircons are rarely found as clear,
gem-quality crystals. The mineral's outer shape is preserved
but the appearance becomes opaque and dull. According to 'Fluorescence
: Gems and Minerals Under Ultraviolet Light', by Manuel Robbins,
trivalent rare earths, particularly dysprosium, praseodymium,
and europium, are suspected in this fluorescence. Since dysprosium
is associated with similar yellow fluorescences, it seems to
be the favorite candidate. (Thanks to Doug Mitchell)
|