PRECIOUS STONES. 181
Faroes, and rarely in Scotland at Usan. Fire Opal is sometimes called Girasol also.
4.
Common Opal includes a considerable number of sub-varieties. In one
form or another it is very common, large masses of hydrous silica
occurring in some parts. As in the case of Chalcedony, the pure kinds
are translucent and colourless, but with the addition of various
impurities many varying forms arise. Milk Opal shows white, bluish, or
greenish tints. Resin Opal, or Pechopal, has a resinous lustre and a
yellow colour. Semiopal is a sub-translucent kind. Hydrophane is a
light coloured variety, which is absorbent enough to adhere slightly to
the moistened finger, and it has the property of becoming more
translucent when placed in water, hence the name.
The more massive forms of Common Opal are ground and polished for much the same purposes as Agate is, e.g., pin
trays, knobs for umbrellas, sleeve-links. Common Opal is found in all
the localities mentioned under Precious Opal, also in Moravia and
Bohemia, at Kosemiitz in Silesia, in Iceland, Ireland, Scotland.
5.
Cacholong Opal is very feebly translucent from the presence of
disseminated mineral matter, which is often zeolitic. It is often
present in Agate alternating with Chalcedony, and such banded specimens
may be used for cameo-cutting. The Faroe Islands may be instanced as
producing very fine specimens.
6. Opal Agate is more correctly included under Agate.
7.
Menilite is a concretionary form found at Menilmontane, near Paris,
embedded in a clayey shale. It is brown or grey in colour, and
sometimes shows alternate bands of these two colours.
