taining vermicular prochlorite inclusions identical with those observed in the large skull described above.
The
amethysts of Guanajuato, which have a world-wide reputation, are found
in large quantities, associated with pink and white apophyllite, and
ranging in color from the most delicate pink to the deepest red. The
crystals are frequently light in color at the base, but very much
darker at the terminations. Groups a foot across, not good enough to
cut gems, are frequently found; it is certain that fine amethysts were
formerly found at some locality in Mexico, since the collections
contain fine objects made by the Aztecs, but not at all resembling the
Guanajuato mineral either in color or structure.
Chalcedony,
agate, jasper, and the other varieties of quartz undoubtedly exist in
abundance at many places in Mexico and Central America, judging from
the numbers of objects, such as beads, figures, and ornaments, in the
collections. Some finely carved agate figures six inches in length are
in the Blake Collection in the United States National Museum, and
similar objects exist in the collections of other museums.
The opal,1
in all its varieties, is found in Mexico and Central America, the
noble opal occurring more frequently in Central America than in
Mexico. The opal consists principally of silica, differing from quartz,
however, in not being crystalline, and in containing from 9 to 12 parts
of water in 100. The specific gravity of quartz is 2.65, of opal about
2.2. Quartz has a hardness of 7, and opal of only 6 and even as low as
5.5.
Noble
opal is the harder variety, in which the color is uniformly
distributed, and ranges from opaque white to almost the pellucidness of
glass. Fire opal or girasol is the variety showing flashes of red and
yellow, green, and other colors, the opal itself ranging from colorless
to white, transparent yellow, reddish-brown to almost opaque, and is
usually less hard than the noble opal. The name lechosos is applied by
the Mexicans to the variety showing deep-green flashes of color. The
name Harlequin is
1
Whatever may be the origin of the widespread notion of the unluckiness
of opal, it is certain that opal was the favorite gem of the Romans,
even in their palmiest days. Since it has become known that Queen
Victoria is partial to it, the old superstition, which it is said may
be traced to Sir Walter Scott's Anne of Geierstein, is slowly yielding,
and the gem has gained much public favor during the last ten years.
