Its
value cannot be estimated. This diamond was obtained at a cost of 8
dollars per carat, for it was obtained under contract with a lot
of other stones. Had it not been discovered until six hours later those
who secured it would not have received it, for the contract would have
expired.
The
"Porter-Rhodes" diamond was found Feb. 12th, 1880, in the Kim-berley
mine. It weighed in the rough 150 carats, and its estimated value is
£200,000. It is of a very fine lustre.
The
" Stewart" diamond was one of the earliest large diamonds found in the
South African fields, its weight in the rough was 288-3/8 carats. It is
of a light yellow tinge. It was found in the year 1872.
The
" Jagersfontein," a diamond weighing, in the rough, 209-1/4 carats was
obtained in this locality ; it was stolen, but recovered by the owner.
The " Du Toit I" and " Du Toit II," the first a gem weighing 244 carats when cut, the other weighed in the rough 124 carats. These were obtained at Du Toit's Pan.
The
" Star of South Africa," better known as the "Dudley," weighed in the
rough 83-1/2 carats, by cutting it was reduced to 46-1/2 carats.
It is the property of the Countess of Dudley. It is the diamond
obtained by Van Niekirk from a native in the early days of the diamond
fields.
Besides
this list, there are a great many other large diamonds of historical
interest that have been obtained from the various diamond fields of the
world, many of these gems are connected with deeds of crime of the
worst character.
CORUNDUM,
. and its gem varieties, Ruby, Sapphire, Amethyst, Emerald, Topaz, Aquamarine, and Asteria.
To
distinguish these from other minerals bearing the same names they are
known as Oriental, thus: "Oriental topaz," "Oriental amethyst," "
Oriental emerald/' " Oriental aquamarine," and " Oriental ruby."
Original^
the words Oriental and Occidental were applied literally, but now they
are used to simply establish the superior quality of the gem or
otherwise, so that Oriental ruby means the true ruby.
Crystalline system = Hexagonal.
Hardness = 9.
Specific gravity = 8'9—4'1G.
Lustre = Vitreous, sometimes pearly on the basal planes.
Cleavage = Basal; that is at right angles to the principal axis of the prism, sometimes perfect.
Composition = Pure Alumina (Al2O3) Aluminium 53'4, Oxygen 46-6 per cent.
Inferior
corundum (not considering emery) contains in some instances as much as
15 per cent, of impurities, these being iron, lime, magnesia, and
silica.
From
a mineralogical point of view the different colours of the varieties of
corundum are of no account, as it is the physical properties and
chemical composition that determine the species, and chemistry has not
yet enabled us to arrive at a satisfactory conclusion as to the cause
of the differences of colour in the several varieties of this
mineral. That the colour is derived from the presence of minute
quantities of metallic oxides appear certain, but this does not account
for the blue colour of the sapphire, or the red of the ruby; yet it is
these very colours that determine the value of these gems and assists
to place them in the category of precious stones.
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