parcels
and forwarded to London, where they are reassorted and supplied to the
trade. The color, size, and quality of the diamonds from the different
mines vary considerably, but are fairly constant for each mine. A
majority of the diamonds from the De Beers mine, for instance, are
"yellows," colorless stones being almost never found there. The
Dutoitspan mine, on the other hand, produces many blue-white and white
stones, and these are generally of large size. The diamonds of the
Jagersfontein mine excel all others in quality, superb blue-white
stones being the rule.
From
the South African mines have been obtained the world's largest
diamonds, unless the mythical "Grand Mogul" and questionable
"Braganza" are to be excepted. The largest and finest of' the South
African stones, also the superior of any other known diamond, is that
called the "Jubilee" or "Excelsior." This stone weighs 239 carats, and
was cut from a crystal of 971| carats found at Jagersfontein in 1893.
It is cut as a brilliant, and has the following dimensions: Length,
I-5/8 inch; breadth, If inch; depth, 1 inch.
Other
noted South African diamonds are the "Tiffany," a yellow diamond
weighing 125-1/2 carats; the " Star of South Africa," already mentioned
as found in 1869, and now cut to a size of 46-1/2 carats; and the "Victoria," a stone of 180 carats, cut from an octahedron weighing 457-1/2 carats.
Turning
to a consideration of the geological characters of the diamond-bearing
areas, it may be stated that each is approximately spherical or oval
in form, with an average diameter of two hundred to three hundred
yards. The four principal mines are embraced within an area four miles
square. The areas in which the diamonds were found were originally
somewhat depressed, giving to them the name of "pans." The upper
portion of the area was a friable mass of a yellow color called "yellow
ground." On going deeper the color of this portion changed to a blue or
greenish blue, and the rock became firmer. It is this "blue" or "blue
ground" which, now that the yellow ground has become exhausted,
furnishes all the diamonds. The strata which inclose it are, as
illustrated in the accompanying figure, at the top, a layer of basalt
about fifty feet in thickness; below this two hundred to three hundred
feet of a nearly horizontal black, carbonaceous shale; next a thin
conglomerate; next about four hundred feet of a dark rock called at
first melaphyre, but now regarded as olivine diabase; and finally a
quartzite which extends as far as exploration has gone. The relation of
the diamond-bearing ground to these strata seems to be in the nature of
a volcanic intrusion. The diamond-bearing or " blue
83
