EMERALD, BERYL, AQUAMARINE. 133
Among
the finest gems of the Pulsky colÂlection is the head of a Syrian king
upon a pale tinted amethyst, engraved with the artist's name NEAPKHS
EMERALD, BERYL, AQUAMARINE.
These
three substances are, in a scientific point of view, very nearly
identical; but in commerce the value of the emerald is infinitely
greater than that of the beryl and aquamarine.
The
emerald, when it possesses a green tint of a beautiful quality, and
when it is entirely hyaline, is one of the most rare and precious of
gems. On the contrary, when it appears in semi-transparent crystals of
a watery green, it is quite common; indeed there are few granitic
mountains where it has not been observed.
The colour so remarkable in the emerald is due to a pretty large quantity, 8 to 9 parts in 100, of oxide of chromium.
The
fundamental form of crystals of emerald is the regular six-sided prism.
As the side of the base nearly always equals the height, the faces of
emerald crystals vary very little from a square.
Another
form which frequently occurs is the twelve-sided prism, which is
derived directly from the primitive form by the modification of the six
vertical edges.
