Many
of the Mexican and some of the Central American opals have the
reputation of fading and becoming translucent, or opaque, or cracking
in course of time, according to the circumstances of the exposure.
Dr.
Hamlin's second instance illustrates this : " A few years ago, some
Spaniards arrived in New York with a bag of rough opals brought from
Central America, but from what particular locality we never learned.
The specimens varied from the size of a bean to that of an English
walnut, and were extremely beautiful. They had a fresh appearance, as
though they had been recently extracted from the mines, and many of
them had portions of the soft, sandy matrix still attached to them.
They excited suspicions of not having been properly tempered and
hardened by exposure. But their beauty, which reminded one of the
perfect glowworm, or lumps of phosphorus moistened with oil, did not
allow the spectator to hesitate about the purchase of them, especially
as they were offered at a moderate price. We invested in the purchase
of several charming ones, and never wearied in examining their
exquisite effects. Still we felt a vague suspicion of the enduring
qualities of our newly acquired treasures. The most beautiful stone,
the size of a small almond, we carried in our pocket for a long time,
not only for our gratification, but for the purpose of studying the
effect of the atmosphere upon its reflections. Soon after the
acquisition, we fancied a slight shadow, or nebulosity, appearing in
one end of the stone. We carefully watched it, and before long an
indistinct cloudiness began to appear, like the dim and distant haze of
a summer sky on the commencement of a storm. Even then, we thought it
might be mere fancy on our part. But when the shadow changed to
opacity, and the transparency of the gem, with its beautiful
reflections, vanished never to return, we were compelled to admit that
even substances of the mineral kingdom had their diseases, as well as
forms of the organic world. This is indeed but one example to
illustrate a theory, but most of those we purchased at that time of the
Spaniards have altered in appearance, and some of them quite as
seriously. Wherefore, we have arrived at the conclusion that recently
mined opals should be bought with caution, and that the perfection of
a rough opal as a gem cannot be
