peculiar
rosy lilac hue which it presents and for its perfect transparency.
Many brilliant and perfect cut stones have been fashioned from this
variety of spodumene, which is found near Pala, in San Diego County,
California, at a locality famous for its lithia minerals, such as
lepidolite, amblygonite and tourmaline. Kunzite, so named after Dr. G.
F. Kunz, the gem expert, resembles the yellow spodumene of Brazil, and
the green spodumene (hidden-ite) of North Carolina, in its
transparency, its easy cleavage, its hardness of 6f, and its specific
gravity of 3'i8, but, unlike these varieties, it exhibits a
characteristic phosphorescence after exposure to the influence of
radium bromide and of the X-rays. As the colour of this mineral is pale
it is seen to perfection only in somewhat large specimens—for example,
in a brilliant-cut stone of 20 carats or more. This is the case with
the precious stone which Kunzite most nearly resembles in hue, namely,
pink topaz.
Opal.
Among
the numerous forms or varieties of the mineral species called opal one
kind alone is prized as a gem-stone. This is the noble or precious
opal, which is distinguished by its play of brilliant rainbow colours.
These are not caused by any coloured substances as constituents, but
are due to a peculiar structure of this mineral. Although by
transmitted light the precious opal appears milky or cloudy and yellow,
by reflected light it exhibits orange, red, blue, green, and many other
beautiful hues. These colours are produced by a mechanical or physical
structure, which consists of a multitude of fissures, the sides of
which are minutely striated, and which causes the diffraction and
decomposition of the white light which falls upon them. The size of
these str'ations and fissures influences the colour and its
distribution within the stone, some specimens showing a predominance of
one set of hues, say red and orange, and others exhibiting chiefly
green, sea green,
S44o.
(J
