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One often hears that diamonds aren't rare at all.

Upon closer inspection, such claims appear to actually state that diamonds cost more than their abundance alone would account for. Sources that outright claim that diamonds are common don't seem to have anything to back it up with. Plus, most sources that state numbers tend to state how many are mined, which is a meaningless number when one considers the possibility of artificially limiting the supply to inflate prices.

So, on a scale of iron being common (~50000 ppm in Earth's crust) and gold being rare (~0.005 ppm), are gem-quality diamonds rare in Earth's crust?

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    An interesting quote from Wikipedia: "Historically, diamonds were found only in [...] India. India led the world in diamond production from the time of their discovery in approximately the 9th century BC to the mid-18th century AD [...] the first non-Indian diamonds were found in 1725" (link) - suggesting that for about 2700 years, diamonds were only found in a single country on the planet. – RomanSt Feb 18 '14 at 0:51
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    @NateEldredge: I had a similar thought about industrial-grade diamonds. Reading through a few of those sources, I found references to "gem-quality diamonds", which I hope will be a close-enough definition. I've edited the question to add it. – Oddthinking Feb 18 '14 at 2:14
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    Iron and gold are elements. Diamond is not. It's not a like-things comparison. – fredsbend Apr 23 '17 at 0:10
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    @fredsbend To be pedantic, diamonds are a specific arrangement of atoms of a single element, so there's a bit of likeness there. (Though while it's possible to create diamonds artificially, you cannot refine them from ore like you can metals). – JAB Apr 23 '17 at 23:06
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    @Jab I don't think that's pedantry as much as it is incorrect. Diamond doesn't behave like carbon, because it's not "just carbon". – fredsbend Apr 24 '17 at 5:00
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Upon closer inspection, such claims appear to actually state that diamonds cost more than their abundance alone would account for. Sources that outright claim that diamonds are common don't seem to have anything to back it up with.

In terms of where diamonds can be found, this is true.

Note that I believe a comparison of diamond production to gold production to be intrinsically flawed. The geological processes which create the deposits of each are vastly different. Gold is actually extraterrestrial in origin, whereas diamonds form from materials already on our planet over billions of years. There is a vast difference in the density of the materials, and gold's value is based solely upon purity of the metal, whereas determining value of a diamond is much more complex, and varies wildly from specimen to specimen.

A much more useful comparison is to other gemstones.

Mindat.org lists 738 localities for diamonds. Compare this to the 20 for benitoite, a very rare gemstone, the 381 localities for ruby, the 284 localities for emerald, or even the 626 localities for sapphire.

Note, however, that locality alone is a poor indicator, as the overall productivity of a mine (amount of desired resource retrieved) can vary significantly, and, given that the full extent of a site's production cannot be measured until it is fully exhausted (and even then it is possible to miss materials).

In 2013, rough diamond production from mines was estimated at 130 million carats. By contrast, in 2005, emerald production was estimated at 5,400kg (27 million carats).

Gem-quality diamonds only account for approximately 25% - 30% of the production of diamond mines*, which would mean that the global production of gem quality diamonds is estimated at between 32.5 million carats and 39 million carats in 2013. By definition, emeralds are gem-quality specimens of the beryl mineral family with a rich, distinctly green color, so 100% of emerald production can be considered gem-quality.

This puts global gem-quality diamond production at roughly 20% greater than emerald production.

Top-quality emeralds, sapphires, and rubies are rarer than top-quality diamonds, and can command a higher price-per-carat, but generally, other qualities of those gemstones are lower than comparable prices for diamonds.

It is difficult to evaluate comparative value vs comparative rarity when discussing gemstones, because the value of individual samples of gemstones varies tremendously based upon the specific characteristics of the specimen. In particular, color, size, and clarity (the amount of, or complete lack of, other mineral inclusions) impact the value of a given gemstone, although other factors such as cut, fluorescence, etc., can also increase or decrease the value.

*note that the proportion of "gem-quality" diamonds seems to be the topic of some debate. Between 3 sources (1, 2, 3), the proportion is respectively 20%, 25%, and 30%.

  • Good answer! I agree that comparing to gold is not ideal, I just needed some way to quantify "rare". – RomanSt May 11 '17 at 22:32
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Total proved diamond reserves worldwide are on the order of 2.6 billion carats. This source provides numbers for some reserves in Russia along with their share in Russia's Reserves Register, giving us a figure of 1.29 billion carats for Russia alone. This same source also states that 80% of this amount is located in Yakutia, and that this amounts to "almost half" of the world's proved diamond reserves. Guessing ~40% as the "almost half" figure, we can infer that the total proved worldwide reserves are around 2.6 billion carats.

Note that these are natural industrial diamond reserves. Only 30% of diamonds are gem-quality. 2.6 billion carats is 520 metric tons, meaning there are ~160 tons of gem-quality diamonds in the known worldwide reserves.

By comparison, the USGS (among other sources) estimates (PDF) the unmined gold reserves at ~57,000 metric tons. Obviously these are only the known deposits, economically mineable – same as with diamonds.

Disregarding the estimated ~150,000 tons of gold already mined (and an unknown amount of gem-quality diamonds), unmined gem-quality diamonds are 300x-400x more rare than gold.

Both of these statistics look only at diamonds/gold that we can extract and hold in our hands. My interest in this started when lots of clickbait articles made it sound like in the absence of De Beers, diamonds would be literally worthless. Considering that they are shiny (when cut) and rather rare, they would certainly be worth a fair amount even without anyone artifically messing with the supply.

P.S. Another thing to consider is that diamonds, unlike gold, are not all equal. By color alone, only about 7% of the natural gem-quality diamonds are of the VVS clarity. D-color (colorless) internally flawless diamonds are estimated to total 0.001% of worldwide diamond production - on the order of 5-6kg in worldwide reserves. Obviously these are ridiculously expensive, De Beers or not.

  • How much does it cost to manufacture a diamond from scratch, at that? en.wikipedia.org/wiki/Synthetic_diamond – JAB Apr 23 '17 at 23:07
  • @JAB Can't find any info on the costs of growing a gem-quality synthetic diamond. Humans being irrational, though, the natural diamonds will probably continue to be valued for their rarity, like gold nuggets which are worth a lot more than their weight alone. – RomanSt Apr 24 '17 at 9:08
  • @RomanSt: Part of the anti-DeBeers claim is that synthetic jewellery-grade diamonds, especially after the Russians started seriously manufacturing them, should have dropped the price of diamonds but instead DeBeers started laser etching "natural" diamonds to keep prices artificially high. Modern artificial diamonds can be made to be indistinguishable from mined diamonds (they are after all the same thing) except by a serial number tracked by diamond distributors – slebetman Apr 26 '17 at 5:09
  • Wow, I'd have thought the percentage would be lower than 30%. – PoloHoleSet Apr 26 '17 at 16:21
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    @TSar Are you referring to the GIA link? They are one of the top diamond grading labs in the world and do a lot of the professional education in gemology. They also developed the 4Cs that are used to grade gem stone quality stones. This is where it gets a bit odd because the definition of gem quality is market driven more so than a geological definition. Gemstones are basically want people make into jewelry, there's not much more to it than that. – rjzii May 3 '17 at 1:33

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