The above may be considered as the types, the composition not being always constant.
The
chemical structure of the six kinds is seen to be identical, the
replacement being by elements of equal chemical value. The group is a
large one, and includes several gem-stones largely used for ornamental
purposes. Some of the varieties are very abundant, and this renders
them of comparatively little value; but many of them nevertheless
possess many qualities that are necessary in precious stones. They are
found of almost every depth of hue and colour, and they also vary much
in hardness and specific gravity. They all crystallize in the cubical
system, are singly refractive, and not dichroic; they are usually found
crystallized as the rhombic dodecahedron, or as the icositetrahedron,
the octahedron being extremely rare.
Besides
the property of cubical crystallization, which belongs to the whole
group, there is another character common to them all, with the
exception of the lime-chrome garnet (ouvarovite), namely, fusibility
before the blowpipe. This test alone is sufficient to determine the
garnet from many stones much resembling it in colour and other
properties; this has been pointed out previously.
The name garnet is (on the authority of Dana) from the Latin granatns (like
a grain), because it is usually found in granular forms, although the
origin of the name is, by some authorities, traced to its similarity to
the seeds of the pomegranate.
The
name carbuncle, by which the garnet is often known, is applied in many
different ways, and is somewhat misleading ; it at one time denotes the
manner of cutting, at other times it is used to distinguish the
almandine or iron-alumina garnet. The ancients gave the name to all red
stones, while modern writers are certainly not more definite in their
use of the word. Theophrastus says it resembles burning coal, and emits
light in the dark. The Hebrew for carbuncle is a word meaning
lightning, and we are told that the Jews have a legend that this stone
was suspended in Noah's Ark to diffuse light. The word is now used to
denote the scarlet and deep red garnets, cut en cabochon. There is no necessity for the use of the word, and it should be discarded.
The
garnet was a favourite stone among the ancients. The Greeks and Romans
were extremely fond of this gem, and used it largely for engravings.
Several specimens are now to be seen in Paris, Rome, and St.
Petersburg. The celebrated Marlborough garnet, engraved with the head
of the dog '• Sirius," is considered to be a masterpiece of this kind
of art. A magnificently engraved stone, contained in the Berlin
collection, is a splendid specimen of the Greek school. The Persians
were very fond of engraving the portraits of their rulers on this
stone. It was largely employed by the Celts and Anglo-Saxons for
jewellery, filigree, and enamel work, slabs of polished garnet of
considerable area being used by them as inlays.
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