Are diamonds rare?
Yes. No. It's actually not as simple as you might think.
All gemstones are rare in contrast to the rest of the earth, but when compared to other gemstones, diamonds are relatively common in nature. You've probably heard of a few stones like alexandrite and tanzanite that are advertised as rarer than diamond, which is true, but the reality is even good ol' sapphire and ruby are considerably more rare.
Now let's put that in perspective.
Here's a favorite quote from Rebecca Pickering, a chief engineer at the now closed Argyle Diamond Mine:
"For every 4 Olympic swimming pools of rocks we crash, we get half a bucket of diamonds."
An Olympic swimming pool is 660,000 gallons. Earth has a density of 5.52 g/cm³, which means that's 30,400,000 pounds of earth, give or take.
I don't know how big Rebecca's favorite bucket is, but assuming it's a standard 5 gallon bucket, and knowing that diamond has a density of 3.5 g/cm³, we can figure that's roughly 73 pounds.
So at an actual mine site, you're expecting to yield 73 / 30,400,000. That's just getting hard carbon out of the ground. That's the easy part!
The vast majority of mined diamonds are not gem quality.
70-80% of all mined diamonds go to industrial uses like drill bits, saw edges, x-ray machines, and computer chips.
So of your 73 pounds of diamond rough, you immediately have to give away 55+ pounds to be turned into power tools.
18 lbs of diamonds is still a lot - over 40,000 carats!
Except...
Only about 15% of all mined diamonds are near colorless, with less than 1% falling in the colorless range.
Likewise, when it comes to clarity, less than 20% of diamonds are VS or above, with only around 0.5% considered flawless.
It's tough to do the math on this since there is overlap.
Color and clarity are mutually exclusive, so you can have a white diamond with lots of imperfections, a clean diamond with lots of yellow, etc.
Assuming you want something fairly white, and clean to the naked eye -not perfect, but pretty- to say you're going to be looking at the top 10% of all gem quality mined diamonds is actually a very conservative figure.
Your 18 lbs of diamonds just became 1.8 lbs.
There are many other factors like fluorescence, country of origin, composition types, etc.
Depending on how picky you are, and assuming you don't want your diamond to be hazy or milky or murky, you're going to lose at least another third.
Call it a pound.
Then there's size.
A huge portion of gem quality diamond is going to become what we call melee. These are the small diamonds (typically anything less than 1/5 of a carat) that are used as accents in jewelry.
It's impossible to know exactly what percentage of diamonds are cut into melee versus larger goods, but a cursory look at the marketplace will show that it is exponentially easier to find, and at significantly lower prices. One carat of melee may cost 1/10th as much as a single one carat diamond in the same quality.
In reality, you're probably going to be down to an ounce or so already, but to be as conservative as possible, we'll pretend it's a 50 / 50 split.
8 oz.
If you have a certain shape in mind, that's going to limit things - especially if that shape isn't round.
You also have to remember that many cutters cut to preserve weight rather than beauty, so if you want a well-cut diamond with life and sparkle, that's rarer still!
Again, it's impossible to give an exact number. If you want a half carat round, they are exceedingly more available than say a three carat oval. We also aren't getting into cutting loss, or crystal structures, or any of the other things that go into play here, but suffice to say that there's no guarantee that your 8 oz of rough diamonds will yield something you want.
To recap, using conservative figures, 4 Olympic pools worth of hypothetical earth yielded us 8 oz of diamond that you might be proud to wear. That then gets dispersed to millions of potential customers across at least 10 major diamond buying countries around the world.
So are they rare?
In the strictest sense, it's difficult to call diamond rare when compared to other gems. However, if you want a decent size and quality with modest imperfections and a nice amount of sparkle, then yes! That can be very rare indeed.
As a final note, all of this is omitting fancy colored diamonds. Natural yellow diamonds are the most common, making up about 60% of all fancy colors, and are thought to be about 10,000x more rare than white diamonds.
Other colors like blue, green, red, and violet are exceedingly rare.
It is thought that only about 30 carats of red diamond have ever been mined, most well under the one carat mark.
If the question is "are natural fancy color diamonds rare?" then this article could have been one word long: Absolutely!