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 (hiddenite) of North Carolina, in its transparency, its easy cleavage, its hardness of 6¾, and its specific gravity of 3·18, 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 striations 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,
