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Diamond values

    Exchange rate between the old and present value is:
    1FF = US$0.195    £1 = US$140.0

  1606     1750     1865     1867     1878    
1 carat   545 202 453 529 110
2 carats   2182 807 1639 2017 350
3 carats   4916 1815 3151 3529 625
4 carats   6554 2470 - - 975
5 carats   8753 5042 8067 8823 1375

The prices current for brilliants of ordinary size at the end of the seventies is best seen from the following table, which was compiled by Vanderheym, on behalf of the syndicate of Parisian jewellers, for the Paris Exhibition of 1878. Two brilliants of weights from 1 to 12 carats and of four qualities were exhibited, and the prices in francs given in the table are for the pair of stones:

Weight (carats) 1st quality 2nd quality 3rd quality 4th quality
1 220 180 150 120
1 1/2 400 300 250 200
2 700 600 480 400
2 1/2 950 800 625 525
3 1250 1020 780 660
3 1/2 1600 1225 945 720
4 1950 1440 1120 960
4 1/2 2350 1642 1305 1080
5 2750 1900 1500 1250
5 1/2 3250 2117 1705 1430
6 3700 2340 1920 1620
6 1/2 4250 2567 2112 1820
7 5000 2765 2310 1995
7 1/2 5800 3000 2550 2175
8 6700 3240 2800 2360
8 1/2 7600 3485 3060 2550
9 8500 3735 3330 2700
9 1/2 9400 3990 3562 2897
10 10300 4250 3800 3050
10 1/2 11400 4515 4042 3255
11 12500 4840 4290 3465
11 1/2 13700 5175 4600 3737
12 15000 5400 4800 3900

The prices given in the above table of course apply only to the time at which it was compiled. A striking feature of the table is the difference, which exists between the prices of stones of the same weight but of different qualities, especially in the case of stones of the first and second waters. The difference between the value of a 1-carat stone of the first water and one of the second water is much greater than between stones of the second and third waters, and in larger stones the difference is still greater. Thus a 1-carat stone of the first water is worth almost three times as much as a stone of equal weight of the second water, the values of stones of this size of the second and third quality being in the ratio of nine to eight. The explanation of the apparent anomaly lies in the fact that in the Cape deposits large diamonds of the first water are rare, while stones of large size but inferior quality are abundant.

A consideration of the table will also show to what a small extent the values of diamonds at the present day are in agreement with the so-called Tavernier's rule, according to which the value of a stone is proportional to the square of its weight. While the value of a 1-carat stone of the first quality would be, according to Tavernier's rule, 110 X 12 X 12 = 15,840 francs, its actual value in 1878, according to the table, was 7,500 francs, or not quite half. The application of the rule to smaller stones results in a calculated value which is still further removed from the actual value; thus the value of a 6-carat diamond of the first water calculated by this rule would be 110 X 6 X 6 = 3,960 francs, while it is actually worth but 1,850 francs. At the present time, this tendency is even more marked than it was in 1878; the value of stones up to 15 carats is approximately proportional to their weight, so that a 1-carat stone is worth about double, and a 3-carat stone about three times as much as a 1-carat diamond. This holds good, at any rate, for the three inferior qualities of stones, but in the case of diamonds of the first water the increase in value is not proportional to the increase of weight.

The price of a 1-carat stone of the first water calculated by Schrauf's rule, according to which the value of a 1-carat stone is multiplied by the product of half the weight of the stone into its weight plus 2, would be 110 X 6 X 14 = 9,240 francs, the tabulated value being 7,500 francs; the value thus calculated, although nearer the mark than in the former case, is still considerably too much. As in the case with Tavernier's rule, the values calculated by Schrauf's rule for smaller stones are still further from their actual value, the calculated worth of a 6-carat stone being 110 X 3 X 8 = 2,640 francs while it is actually worth but 1,850 francs. At the present time the market price of a fine 1-carat brilliant is £15; in exceptional cases, however, £20 to £25 may be given for such a stone.

The price of stones of exceptional size, that is of those weighing anything over 1-carats, is not governed by rule, and depends very much on what a rich person or State is disposed to give for them. Diamonds of exceptional size and of unusual colours are not common articles of commerce, and their price, while always, of course, very high, depends on the number of would-be purchasers, which can be found for them.

With regard to the prices current for smaller diamonds, it is impossible to say much more than has been already said, for, after all, the value of stones of ordinary size depends to a very large extent on their quality. The price of cut gems and of rough stones always differs very widely; the latter are not, as a rule, bought and sold singly but come into the markets in large parcels, those from the Cape being carefully sorted and arranged according to quality, while parcels from Brazil consist of unsorted stones of all qualities.

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Rafal Swiecki, geological engineer email contact

This document is in the public domain.

March, 2011