serpentinous
decomposition product at Koserniitz in Silesia, specimens from which
showed 0'5 to 1"0 per cent, of nickel oxide on analysis. The colour is
destroyed by moderate heat and also by strong light; if used as a seal
to any great extent much of the colour is discharged, but it can be
regained to a large degree by soaking the stone in water ; the colour
is supposed to be due to nickel in the form of a hydrous silicate, and
colourless Chalcedony can be made to very closely simulate Chrysoprase
by impregnating it with a solution of a green nickel salt. There is a
locality where it occurs in India, but it is not known definitely, and
other occurrences, though widespread, are not of great importance. At
one time it was a very fashionable stone, then its use almost entirely
died out, but in recent years it has again come somewhat into favour.
It is usually cut in a low rounded form, often with one or two rows of
facets above the girdle.
4.
Prase is a dark green variety ; some forms of crystalÂline Quartz of
the same colour are also known as Prase. It is translucent, and owes
its colour to fine filaments of Actinolite as a rule. It was a
favourite substance for engraving in Roman times, and is still
sometimes so used ; also cut into flat pieces for inlaying. Saxony and
Scotland may be mentioned as two of the numerous localities. This was
the Heliotrope of Pliny.
5.
Plasma is a form of Chalcedony containing a chloride or asbestos-like
mineral, or what is known as Green Earth (Delessite or Saponite). It
was the Iaspis of Pliny in part. In colour it varies from a dull
leek-green to almost emerald-green, often showing white spots. It was
fashioned by the Romans, but now is seldom used; the best specimens come
