First of all, the analyses of rare-earth impurities in natural
fluorites have been reported by several investigators [2-5].
The fluorite structure readily incorporates many impurity
ions, some of which have been purported to cause
color. REEs are very common impurities in fluorite,
along with certain transition elements, because they are
similar in terms of ionic size and charge state to
calcium. Electronic transitions involving electrons from
the d and f orbitals of these elements are a major cause
of color in minerals including fluorite [6].