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NATURAL HISTORY OF GEMS.
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arrows
or hammers) penetrated into the earth to the depth of nine fathoms, and
then rose up towards the surface at the rate of one fathom in a year.
De Boot quotes many similar instances of their discovery under the same
circumstances, but, unable to resist the evidence of human
workmanship which they exhibit, ingeniously conjectures that they had
been originally iron tools, but converted into stone by long
continuance in the earth !
The Iris, mentioned
by Pliny as next in estimation to the Ceraunia in the opinion of the
Magi, was nothing more than a piece of Rock-crystal which had
accidentally assumed the form of a prism, so that within a room it was
capable of forming the prismatic spectrum upon the wall. A most
beautiful phenomenon truly, and well adapted to excite a belief in the
supernatural virtues of the medium in the minds of people ignorant that
the effect was due merely to the form. It was remarked as
strange, that when placed in the sun the arrangement of its angles did
not produce the rainbow colours, but only when under the shade of a
roof. Pliny observes that the stone itself did not contain the colours,
but that they were elicited by the reflection of the wall. In all other
respects it resembled common Rock-crystal : it was found in an island
in the Eed Sea, sixty miles off Berenice.
There was another gem resembling this in appearance, but not in effect, and therefore called Leros (empty), which was a Crystal crossed by a white and black cloud.
The gem now known as the Iris is
Rock-crystal containing many natural flaws, which by the refraction of
light produce the most beautiful play of colours internally,
resembling sheets of flame. The Iris can be artificially created by
flawing the Crystal with a sharp blow of a mallet, or by throwing it
into boiling water.
Besides the Ceraunia, Pliny (65) enumerates other stones
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