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140
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GEMS.
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How long does Nature take for this operation ?
This can never be determined.
Wood petrifies into silex, agate, and chalky substance.
The bushes which surround the so-called Lago dei Tartari, which is in the Tibertine territory, petrify from year to year.
It
is not long since a beam of timber was found under the bed of the
Danube ; it had been used in the construction of the Emperor Trajan's
bridge over that river, and it was found that in 1,500 years it was
only petrified 3/4ths of an inch from the circumference towards the
centre.
Agate
wood has a concave and rough breakage ; it acquires a resinous light ;
it cuts crystal, and has a specific gravity between 2-53 and 2"65.
This substance is sometimes opaque, at other times it is transparent, but more frequently translucent.
It
is easily worked as its texture yields to every tool ; it is therefore
used in making vases, snuff-boxes, knife-handles, and seals.
It is generally worked in Germany, and in the same way as the agates of Oberstein,
LYII.
LEPIDOLITE
Is a sort of mica with a base of lithia, thus named from the Greek lepis, scale, and λίθος, stone, because, in general, it is found under the form of small pebbles,
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