DIAMOND in SOUTH AFRICA
Dry Diggings (suite)
The average value of stones from the different mines of course varies in correspondence with the variations in quality we have just been noticing. In the first column of the following table, compiled from the estimates given by Moulle, will be found the average price per carat of rough stones from the different mines during the period between September 1, 1882, and the end of March 1884. The corresponding prices for 1887, given in the second column, are somewhat lower, but the proportion existing between them is about the same and has indeed remained practically unaltered up to the present day.
These four mines yield, on an average, respectively, O.77, 1.O5, 3.15, and 4.55 carats of diamonds per cubic metre of "blue ground," so that the stones found in mines of which the yield is poor, surpass in quality those found in richer mines.
In the Jagersfontein mine, as has been already mentioned, are found the whitest, largest, and most transparent of Cape diamonds, some of which approach, or even equal, the beautiful blue-white Brazilian and Indian stones which are so highly prized. The abundance of white stones in this mine is sometimes thought to be connected with the complete absence of pyrites, which is found everywhere else and has been supposed to be the cause of the yellow colour of Cape diamonds. The beauty of these white stones is unfortunately, however, often impaired by the presence of spots and blemishes of various kinds; moreover, in addition to regularly and symmetrically developed crystals, irregular intergrowths are not infrequently met with, so that a considerable proportion of stones from this mine are unsuitable for cutting and have to be discarded. The stones found here which are free from faults are of singular beauty; they are comparable to the diamonds of Bagagem in Brazil and command the very highest price.
It has not hitherto been mentioned that the Kimberley and De Beer's diamonds are supposed to be less hard than stones from Du Toit's Pan and Jagersfontein mines and from the river diggings.
The whole of the South African diamond trade centres round Kimberley. The stones usually change hands in large lots and are often placed on the market directly they come from the washing machinery. In other cases they are first sorted into parcels containing various qualities; this process offers great scope to the skill and discretion of the diamond merchant, for the amount obtained for a lot of stones depends largely on the arrangement of the stones of different size, quality, colour, etc. , into parcels.
Various trade names for different kinds and qualities of diamonds have been evolved side by side with the development of the traffic in these stones. Only about four such terms were originally in use; a much greater number are at present in existence, and the significance of some of the most important will now be given below.
Crystals or Glassies are white, or nearly white, perfect octahedra.
Round stones are crystals with curved faces; these are sub-divided according to colour into Cape white, first by-water, and second by-water.
Yellow clean stones is a term which includes all yellow stones, these being grouped according to their shade of colour into off-coloured (the lightest shade), light yellow, yellow, and dark yellow.
Mêlé is a term applied to crystals varying from white to yellow (by-water) and often also to brown, weighing on an average not more than 1 1/2 to 1 3/4 carats. The term "small mêlé" is applied to similar stones as small as 1/20 carat. All stones characterized by this term are round or glassies, never broken fragments.
Cleavge is the term applied to crystals containing spots, to twinned crystals, and to others, which need to be cleaved before they can be cut; thus the term "black cleavage" is applied to stones which, in the rough condition, appear much speckled, but which, after cleaving, give fine stones. Large blackish diamonds are referred to as "speculative stones"; their value depends on their size and on the probability of obtaining good cleavage fragments from them. For stones of this sort (cleavage) weighing less than 3/4 carat the trade name is Chips.
A collection containing black cleavage, stones of a brown or poor yellow colour and bort, forms a "parcel inferior", the contents of which are unsuitable for cutting and are pulverized for grinding powder or applied to other technical purposes.
The London jeweller, Mr. Edwin W. Streeter, in his book "Precious Stones and Gems", gives the following list of trade names for the various kinds of rough Cape diamonds: (this differs somewhat from that given above)
Rafal Swiecki, geological engineer email contact
This document is in the public domain.