170 Agate.
The
mocha- or moko-stone is a variety containing infiltrated dendritic
oxides of manganese and iron, which give it the appearance of
containing vegetable remains. It is found in Arabia, and is said to
derive its name from Mocha; others suppose the name mocha-stone to be a
corruption of moschas, or moss-stone.
Agate.
The
agate (another variety of chalcedony) is of different colours,
arranged in bands of various thicknesses, often variegated in small
masses in a matrix of chalcedony. When the lines are thin and zigzag,
it is called fortification agate, from its fancied resemblance to the
outlines of a fortification; when in nearly straight lines, it is
called ribbon agate; when containing apparent marks of vegetation, moss agate.
This
stone is manufactured into articles of utility as well as ornament; it
is much used for making burnishers, mortars for chemical purposes,
balances of scales (where great nicety is desired), cups, vases,
seal-handles, etc. It may be coloured artificially, in the same manner
as the onyx.
The
principal manufactories are at Oberstein, where, however, the supply
has fallen off. The rough stones are now brought from the Brazils,
India, Australia, etc., coming to Hamburg and other ports in ships with
light cargoes as ballast. The numerous specimens termed Brighton, Isle
of Wight, Aberystwith, and Irish pebbles,
