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138
GEMS.
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LV.
LAVA.
This natural
production is the spontaneous union of various stony substances which
volcanoes eject during their eruptions, and which, in a state of pasty
fusion, flow like torrents down the sides of mountains, and sometimes
to great distances.
Lava has a broken and concave breakage ; a resinous light ; it is opaque, and is found of almost all colours.
It often contains crystals of felspar, of leucite, of garnet, and of other minerals.
The
blue lava of Vesuvius has the appearance of the blue, transparent,
artificial enamel, and is in much request for jewellery and ornaments.
Even cameos are made from it.
Where it most abounds, as in Naples, they use it to
make vases, candlesticks,, boxes, and other similar articles
Lava is cut with iron, emery, and sand; and is polished with pumice, olive oil, and tripoli.
The graving tool is used in working on the cameo, as well as on shells.
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