This stone exhibits many varieties of color and of composition. The
color probably most often thought of in connection with it is dark red,
but it would be a mistake to suppose this the only color which it may
manifest. Green, red, rose and brown are other colors which garnet
transparent enough to be used as gems exhibits, while among opaque
garnets may be found black and many varieties of the shades above
mentioned.
These variations of color are more or less connected with differences of
composition which it may be well first of all to consider. Garnet as a
mineral is, like most minerals used as precious stones, a silicate.
United with the silica the element most commonly occurring is aluminum.
If calcium be united with these two the variety of garnet known as
grossularite, or essonite, or cinnamon stone, is produced. If magnesium
takes the place of calcium, then pyrope is formed. If iron, we have
almandite, and if manganese, spessartite. Another variety of garnet,
andradite, is composed of calcium and iron in combination with silica,
and still another, uvarovite, of calcium, chromium and silica. Though
they seem to differ so much in composition, all kinds of garnet
crystallize in the same system and are closely allied in all their
properties, so that it is always an easy matter to distinguish garnet of
any variety from other minerals.
Garnet crystals may be of the twelve-sided form, known as dodecahedrons,
the faces of which have the shape of rhombs, or the twenty-four-sided
form known as trapezohedrons, the faces of which have the shape of
trapeziums. Quite as commonly occur crystals which are combinations of
these two forms, and then exhibit thirty-six faces, as in the crystal
from Alaska shown in the accompanying illustration. Sometimes the
crystals attain considerable size, some perfect ones from Colorado
weighing fifteen pounds, while crystals two feet in diameter are
reported from North Carolina. A curious feature of garnet crystals is
that of often inclosing other minerals. The garnets from New Mexico, for
instance, when broken open are sometimes found to contain a small grain
of quartz. In the crystals from East Woodstock, Maine, only the outside
shell is garnet and the interior is calcite. Other crystals are made up
of layers of garnet and some other mineral.
Garnet has a strong tendency to crystallize, and hence is usually found
as crystals. The grains of garnet found in the sands of river beds and
on beaches, though not often showing crystal form, may be really
fragments of crystals. Garnet is one of the most common constituents of
such sands because of its hardness and power of resisting decay. These
properties enable it to endure after the other ingredients of the rocks
of which it formed a part have been worn away. It is quite heavy as
compared with the quartz of which the sand is mostly composed, and hence
continually accumulates on a beach, while the quartz is in part blown
away. In such localities it will always be found near the water line,
because the waves, on account of its weight, can carry it but a slight
distance inland. Practically all garnet is three and one-half times as
heavy as water, and some four times as heavy. Garnet, as a rule, is
somewhat harder than quartz, its hardness being 7½ in the scale of which
quartz is 7. Some varieties are, however, somewhat softer. The hardness
of garnet and its uneven fracture are properties which give it an
extensive use for rubbing and polishing wood. For this purpose it is
spread upon glued paper in the manner of sandpaper and is used
similarly, but it is superior to the latter. Most varieties of garnet
fuse quite readily before the blowpipe, and the globules thus formed
will be magnetic if the garnet contains much iron. The green garnet,
uvarovite, is almost infusible, however. Garnet is not much affected by
ordinary acids, although it may be somewhat decomposed by long heating.
[Illustration: GARNET.
LOANED BY FOOTE MINERAL CO.]
Top row:
Almandite (Colorado.)
Almandite (Connecticut.)
Center:
Essonite (Italy.)
Garnet in Matrix, polished (Mexico.)
Garnet (Hungary.)
Bottom:
Garnet in Matrix (Alaska.)
Uvarovite in Matrix (Canada.)
The name garnet is said by some authorities to come from the Latin word
granatus, meaning like a grain, and to have arisen in allusion to the
resemblance of its crystals in color and size to the seeds of the
pomegranate. The German word for garnet, granat, is the same as the
Latin word. Others think the word derived from the Latin name of the
cochineal insect in allusion to a similarity in color.
The use of garnet for gem purposes seems to date back to the earliest
times. Among the ornaments adorning the oldest Egyptian mummies there
are frequently found necklaces containing garnet. The Romans prized the
stone highly, and it is a gem very largely used at the present day, its
hardness and durability and richness and permanency of color giving it
all the qualities desired in a precious stone.
Two varieties of garnet, almandite and pyrope, may exhibit the dark
blood-red color especially ascribed to garnet. Almandite or almandine
garnet derives its name from Alabanda, a city of Asia Minor, in the
ancient district of Caria, whence garnet was first brought to the
Romans. The finest almandite for a long time came from near the city of
Sirian, in the old province of Pegu, Lower Burmah. While this was the
center of supply, it is not known just where the garnets were obtained.
Such garnets are still known as “Sirian” garnets. Their color tends
toward the violet of the ruby and gives them a high value. There are
several localities in Northern India where almandite is mined on a large
scale, and the stone is much used in Indian jewelry. Some of these
localities are Condapilly, Sarwar and Cacoria. Almandite is also found
in Brazil, in Australia, in several localities in the Alps, and in the
United States. Stones from all these regions are found suitable for
cutting, the only qualifications needed being sufficient size and
transparency and good color. The almandite of Alaska shown in the
accompanying plate occurs in great quantities near the mouth of the
Stickeen river, but has not been extensively cut on account of its being
too opaque. Almandite usually occurs in metamorphic rocks, such as
gneisses or mica schists; also in granite. It is also found in many gem
gravels. From the ruby it can be distinguished, as can all varieties of
garnet, by its lower hardness and single refraction of light. In
artificial light, too, it borrows a yellow tint, rendering it less
pleasing, while the color of ruby grows more intense.
Pyrope, the magnesian variety of garnet, does not differ much in color
from almandite. Both are dark red, but while almandite tends toward a
violet tone, pyrope shades toward yellow. Pyrope is lighter than
almandite, the specific gravity being 3.7 to 3.8, while that of
almandite is 4.1 to 4.3. It is also less easily fusible. It rarely
occurs in crystals, and where found in place is always associated with
the magnesium-bearing rocks, peridotite or serpentine.
It is thus probably always of eruptive origin. Pyrope is a
characteristic constituent of the diamond-bearing rock of South Africa,
and is the stone known in trade as “Cape ruby.” These garnets afford
many excellent gems. The home of the pyrope, however, is and has been
for many centuries, Bohemia. Here it is found in many localities, but
chiefly in the northwestern part, near Teplitz and Berlin. The garnets
are found in a gravel or conglomerate of Cretaceous age, resulting from
the decomposition of a serpentine. Sometimes, however, they are found in
the matrix and often associated with a brown opal. They are found by
digging and separated by washing. Though of good quality the scones are
small, those as large as a hazel nut being found but rarely. Although
the Bohemian garnets have been known for many centuries, the industry of
mining and cutting them on a large scale is said not to have assumed any
special proportions until the advent of foreigners to Karlsbad. In this
way a knowledge of the stones went out to other countries, and a demand
sprang up which has led to the establishment of a great industry and
made Bohemia the garnet center of the world. There are over three
thousand men employed at the present time simply in cutting the stones,
and if to these be added the number of miners and gold and silver smiths
occupied in the mining and mounting of the garnets, it is estimated that
a total of 10,000 persons are engaged in the Bohemian garnet industry.
The stones are used not alone for jewelry and for ornamenting gold and
silver plate, but also extensively for watch jewels and for polishing.
Excellent pyropes are found in Arizona, New Mexico and Southern Colorado
in our own country. They occur in the beds of streams as rolled pebbles,
and often associated with the green chrysolite or peridot of the
eruptive rock from which they came. They are especially abundant about
anthills, being removed by the ants because their size stands in the way
of the excavations of the busy insects. The name pyrope comes from the
Greek word for fire, and is applied on account of the color of the
stone.
Of quite similar origin is the name carbuncle, a term applied to nearly
all fiery red stones in Roman times, but now used to designate garnets
cut in the oval form known as cabochon. The word carbuncle comes from
the Latin word carbo, coal, and refers to the internal fire-like color
and reflection of garnets.
The calcium-aluminum variety of garnet, grossularite, cinnamon stone or
essonite, is less used in jewelry than those above mentioned. It is
usually yellow to brown in color, but may be rose red or pink, as in the
specimen from Mexico shown in the accompanying plate. The yellow
grossularites resemble in color the gem known as hyacinth and are
sometimes sold in place of the latter, but true hyacinth is much heavier
and doubly refracting. About the only essonites or cinnamon stones
available for gems come from Ceylon. These are of good size and color.
Those from Italy, shown in the accompanying plate, are too small to cut
into gems, but surrounded as they are by light green chlorite and
pyroxene, they make very pretty mineral specimens. Grossularite is
almost always found in crystalline limestone.
Green garnets are of two kinds, the calcium-iron garnet, known as
demantoid, and the calcium-chromium garnet known as uvarovite. The
demantoid garnets come only from the Urals. They have a rich green color
and make beautiful gems when good ones can be found. The name demantoid
refers to the diamond-like luster which they possess. The stone is also
known as “Uralian emerald.” Uvarovite, named for Count Uvarov of Russia,
also makes valuable gems if found in pieces of sufficient size and
luster. It is found in Russia, in Pennsylvania and in Canada. Garnet has
long been the birthstone of the month of January.
“By her who in this month is born
No gems save garnets should be worn.
They will insure her constancy,
True friendship and fidelity.”
Such are the virtues ascribed to the garnet. That the stone has been
known and used from the earliest times I have already remarked. Under
the name of carbuncle mention is made of it in the literature of all
ages, its impressive feature being usually the brilliant, fiery light
which it gives forth. According to the Talmud, the only light which Noah
had in the ark was afforded by a carbuncle, and there are many Oriental
tales regarding the size and brilliancy of carbuncles owned by the
potentates of the East. Occasionally carbuncles were engraved, and some
fine garnet intaglios are still known. The greater abundance of the
stone in modern times has led to its being less highly prized than
formerly, and to its being put to other uses than mere adornment, but it
perhaps contributes more largely to the comfort and happiness of the
world as it is now used than could ever have been the case when it was
the property only of kings.
Oliver Cummings Farrington.