Very beautiful examples are known to occur in the environs of
Carthagena, Spain ; but India, and notably the Island of Ceylon, afford •'he best crystals. It is abundant in large masses in
the United States, several localities furnishing excellent specimens for cabinet use.
Agate. — This stone, says Mr. Streeter, does not strictly
belong to mineralogy, which deals with simple minerals. It is a
conglomerale of certain quartz varieties, which, in color, texture, and translucency, are diverse, one from the other, as chalcedony, carnelian, jasper, and some others. When two or more
of these precious stones form a cohesive mass and are arranged
in stripes and spots, the combination is called agate. Some
writers represent the agate as forming a group of gem-minerals,
including nearly all the quartz varieties, a classification not
generally adopted. In composition, it consists of ninety-eight
per cent of silica ; its different colors are supposed to be due
to the presence of iron, manganese, bitumen, and chlorite.
The beauty of the agate depends chiefly upon the character of
the alternate layers of chalcedony and other varieties of quartz,
of which it is composed, whether they are translucent, brilliant,
of fine color, and capable of high polis*h.
Agates, in their native state, are frequently found in the
cavities of igneous rocks caused by the escape of gas or steam,
it is conjectured, when these rocks were in a fluid state.
These cavities were subsequently filled with silica or some
other mineral substance held in solution and deposited on the
interior walls of these receptacles, thus often forming a kind of
geode. These balls are sometimes furnished with a small
funnel through which the silicious matter penetrated.
There are numerous varieties, dependent upon the arrangement of the layers or other incidental causes: as, when the
stone presents delicate parallel lines of light and dark tints, it
