LXX.
ONYX.
A variety of
quartz having a regular alternation of strata more or less even, and
variously coloured in black, white, brown, grey, yellow and red.
Its name comes from the Greek word òvvi, nail, on account of the similarity which is found to exist between the arrangement of its strata and that of the human nail.
When
an onyx has one or two strata of red carnelian it is more valued, and
takes the name of sardonyx. In the onyx the dark strata are always
opaque, and contrast strongly with the clear, which, when thinned,
become almost translucent.
There are Oriental and Western onyx.
The
Oriental onyx is extremely hard, and of very fine texture ; acids have,
in general, very little action on it. When in this mineral substance
are found united neat lines, straight strata, and bright colours, it is
of a relatively high price, especially if it has more than four fillets.
The
Western onyx, and especially that from Germany, is softer than the
Oriental, and is deteriorated by acids, which alter the colour.
Industry turns this peculiarity
