From
the above it will be seen that the name garnet embraces a large number
of different gems, having affinities principally in the chemical law
governing their composition, and in their constant crystalline form.
The
common garnet is supposed to be known to everyone. As a rule we may
consider it to belong to the iron-alumina variety, but there is no
reason to suppose but that specimens of the other varieties may at some
time or other be found in this Colony.
Undoubted
specimens of the magnesia-alumina garnet (pyrope) would be of value if
found, and good almandine or precious garnets would certainly be worth
finding. In a paper read before the Royal Society of N. S. Vales, the
author described precious garnets found at Pyrmont, Sydney ; they are
however very small. The garnets from the M'Donnell Ranges of South
Australia (the so-called Australian rubies) are much too dark, and are
deficient in "fire," yet with these defects their value as rough uncut
stones was in the year 1883 set down as equivalent to 23s. per pound,
so that these inferior .garnets have some commercial value. One often
sees in the jewellers' shops, these gems cut for rings, &c, and
labelled as Australian rubies. Although deficient in colour, lustre,
and brilliancy to the ruby, yet they are real stones and preferable to
paste gems.
Common
garnets are so plentifully distributed, that none but the superior
kinds are worth consideration from a commercial point of view. In New
South "Wales garnets are found in many localities, some good
crystallized specimens being obtained at Broken Hill; they are also
found throughout the Colony, principally at the mining centres. It is
unnecessary to enumerate the very large number of New South "Wales
localities from which the garnet has been recorded.
TOPAZ.
Crystalline system—Rhombic. Hardness—8. Specific gravity—3'4-3'G. Lustre—Vitreous.
Cleavage—Parallel
to the basal plane, highly perfect. Composition—Silicate of alumina,
and fluoride of silicon, silica 1G 2, silicic fluoride 28T, alumina
55"7 per cent.
The
word topaz is supposed to be derived from Topazion, an island in the
Red Sea, as stated by Pliny ; but the topaz mentioned by him was not
the same stone that we call topaz, as it yielded to the file, and had a
hardness less than 7. It was most probably the same gem now known as
chrysolite or peridot, because topaz was not known as a distinct stone
until comparatively modern times.
The
topaz is one of the few precious stones containing fluorine; in fact,
the presence of this element is most rare in this class of minerals.
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