nce" is self-suggesting as to its origin, which is the "noble"
or "precious" opal; this radiates brilliant and rapidly changing
iridescent reflections of blue, green, yellow and red, all blending
with, and coming out of, a curious silky and milky whiteness, which is
altogether characteristic. The moonstone is another example of this
peculiar feature which is possessed in a more or less degree by all the
stones in the class of pellucid jewels, but no stone or gem can in any
way even rival the curious mixture of opaqueness, translucency,
silkiness, milkiness, fire, and the steadfast changeable and prismatic
brilliance of colour of the precious opal. The other six varieties of
opal are much inferior in their strange mixture of these anomalies of
light and colour. Given in order of value, we have as the second, the
"fire" opal with a red reflection, and, as a rule, that only. The third
in value is the "common" opal, with the colours of green, red, white and
yellow, but this is easily distinguishable from the "noble" or
"precious" variety in that the common opal does not possess that
wonderful "play" of colour. The fourth variety is called the
"semi-opal," which is really like the third variety, the "common," but
of a poorer quality and more opaque. The fifth variety in order of
value, is that known as the "hydrophane," which has an interesting
characteristic in becoming transparent when immersed in water, and only
then. The sixth is the "hyalite," which has but a glassy or vitreous
lustre, and is found almost exclusively in the form of globules, or
clusters of globules, somewhat after the form and size of bunches of
grapes; hence the name "botryoidal" is often applied to this variety.
The last and commonest of all the seven varieties of opal is somewhat
after the shape of a kidney (reniform), or other irregular shape,
occasionally almost transparent, but more often somewhat translucent,
and very often opaque. This seventh class is called "menilite," being
really an opaline form of quartz, originally found at Menilmontant,
hence its name (_Menil_, and Greek _lithos_, stone). It is a curious
blue on the exterior of the stone, brown inside.

History records many magnificent and valuable opals, not the least of
which was that of Nonius, who declined to give it to Mark Antony,
choosing exile rather than part with so rare a jewel, which Pliny
describes as being existent in his day, and of a value which, in present
English computa