CHAP. 52.—IRIS; TWO VARIETIES OF IT.
The next name mentioned by these authors is that of the stone called “iris;”3201 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 brightness3202 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.