ndergo a spontaneous
crystallization by slow dessication, which commences the moment the
rock is exposed to the air.

The coloring matter of the emerald seems to be derived from the
decomposition of the remains of animals who have lived in a bygone
age, and whose remains are now found fossilized in the rock which
forms the matrix of the gem. This rock in Granada is a black
limestone, with white veins containing ammonites. Specimens of these
rocks exhibiting fragments of emeralds _in situ_, and also ammonites,
are to be seen in the mineralogical gallery of the Jardin des Plantes
in Paris. Lewy believes that the beautiful tint of these gems is
produced by an organic substance, which he considers to be a carburet
of hydrogen, similar to that called chlorophyll, which constitutes
the coloring matter of the leaves of plants; and he has shown that
the emeralds of the darkest hue, which contain the greatest amount
of organic matter, lose their color completely at a low red heat,
and become opaque and white; while minerals and pastes which are
well known to be colored by chromium, like the green garnets (the
lime-chrome garnets) of Siberia, are unchanged in hue by the action of
heat.

Since the time of the Spanish Conquest, New Granada has furnished
the world with the most of its emeralds. The most famous mines are at
Muzo, in the valley of Tunca, between the mountains of New Granada and
Popayan, about seventy-five miles from Santa Fe de Bogota, where
every rock, it is said, contains an emerald. At present the supply of
emeralds is very limited, owing to restrictions on trade and want of
capital and energy in mining operations.

Blue as well as green emeralds are found in the Cordillera of the
Cubillari. The Esmeraldas mines in Equador are said to have been
worked successfully at one period by the Jesuits. The Peruvians
obtained many emeralds from the barren district of Atacama, and in
the times of the Conquest there were quarries on the River of Emeralds
near Barbacoas.

Emeralds are found in Siberia, and some of the localities may have
furnished to the ancients the Scythian gems which Pliny and others
mention. In the Wald district magnificent crystals have been found
embedded in mica-slate. One of these--a twin-crystal, now in the
Imperial Cabinet at St. Petersburg--is seven inches long, four inches
broad, and weighs four and a half pounds. There is another mass in the
same collection which measures fourteen inches long