CHAP. 52.—IRIS; TWO VARIETIES OF IT.
The next name mentioned by these authors is that of the
stone called "iris;"[1] which is found, in a fossil state, in a
certain island of the Red Sea, forty miles distant from the city
of Berenice. It is partly composed of crystal, and hence it is
that some have called it "root of crystal." It takes its name
"iris" from the properties which it possesses; for, when
struck by the rays of the sun in a covered spot, it projects upon
the nearest walls the form and diversified colours of the rainbow;
continually changing its tints, and exciting admiration
by the great variety of colours which it presents. That it is
hexahedral in form, like crystal, is generally agreed; but some
say that it is rough on the sides and of unequal angles;
and that, when exposed to a full sun, it disperses the rays
that are thrown upon it, while at the same time, by throwing
out a certain brightness[2] before it, it illumines all objects
that may happen to be adjacent. The stone, however,
as already stated, only presents these colours when under
cover; not as though they were in the body of the stone
itself, but, to all appearance, as if they were the result of the
reflected light upon the surface of the wall. The best kind is
the one that produces the largest arcs, with the closest resemblance
to the rainbow.
"Iritis" is the name of another stone, similar to the last in
all other respects, but remarkable for its extreme hardness.
Horus says, in his writings, that this stone, calcined and triturated,
is a remedy for the bite of the ichneumon, and that it is
a native of Persia.