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BOOR VI
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129
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Topazius is
soft and the only one of the precious stones that wears away with use.
It can be scratched by a file and is polished with other rocks and
flint.
Nilios that is found on the banks of the Nile and takes its name from this river is not as beautiful as topazius. It has a smoky topazius or
honey color. When looked at carefully it has a dull, shallow and false
luster. According to Pliny it is found in India, according to Juba in
Ethiopia and according to Sudines along the Severus river in Attica.
The callais or augites gem is of less value than the topazius, according to Pliny, who has written in detail regarding it. This stone is pale green and, characteristically, occurs with topazius. It
is found in large masses, full of holes and dirt, in the hinterland of
India in parts of the Caucasian mountains inhabited by the Phicari and
Asdathae. The stones from Carmania are purer and better. Here they are
found on the sides of unscalable and icy cliffs standing out like eyes
and adhering loosely to the cliffs as if they had been placed there and
not as if they had formed with the rock. To climb these cliffs tires
the people, whether they are on foot or horseback, and the danger
frightens them. Therefore they work around the base, at some distance
from the cliffs, and shake the stones from the moss found there. Luck
varies in the search. Sometimes with one blow they may recover many
fine stones and at other times with many blows they recover none. The callais is
prepared for market in the following manner. They are shaped by cutting
since they are fragile and the best have the color of smaragdus. It
would appear that this stone is regarded so highly because it is
foreign. It is usually set in gold and is no more pleasing than the
gold itself. Oil, ointment or wine will destroy the color of the more
beautiful of these stones. The poor stones are not affected. This gem
can be imitated with glass.
There are stones they say are found in the nests of birds in Arabia that are called melancoryphus. Only that.
In summary, the green transparent gems are smaragdus, beryllus, prase, topazius, nilios and callais. They are distinguished from one another by color, brilliancy and form. Smaragdus, because of its deep green color, is easily distinguished from prase, topazius, nilios, almost all varieties of beryllus and from the pale green callais. Since it tints the surrounding air with its brilliancy it can be distinguished from the finest beryllus and callais. They can be identified by form. Artificers give a hexagonal form to beryllus, the form of an eye to callais while smaragdus has neither of these forms being cut usually in a high cabochon. The first species of beryllus has a different color than all other green gems and has a different form than callais. Chrysoberyllus and chrysoprasius are not always hexagonal and the small stones are cut with a tabular form today. They are easily distinguished from topazius since
they do not have as high a luster. Prase may be either pure leek-green
in color or have blood-red spots or distinctive white veins through it
and thus differs from all the other
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