D&D 5E (2014) Calculating a fist-sized diamond

[Maxperson]

A fist-sized diamond of good gem quality is unique and huge

But it's no Arkenstone

 

[EzekielRaiden]

Could you please tell me how much a diamond the size of a baby's fist would be? I very much would like to know.

Infant hands are small but chubby, making them a bit closer to a sphere than a typical adult's hand. I'd peg them at very very roughly a 1.5 cm radius sphere, or about 14.1 cm^3. Since diamond has a density of about 3.51 g/cm^3, that's roughly 49.6 grams of diamond. Assuming the diamond weighed that much after cutting, it would be approximately 248 carats. The Centenary Diamond is 273 carats, which is close enough for our purposes (we're working with gross approximations anyway). It's estimated to be worth about $100,000,000. (Note that this demonstrates the nonlinearity of carat weight to dollar value: the Greater Star of Africa isn't even twice as large, but best estimates put it at least four times as valuable as the Centenary Diamond.) I'd estimate the baby-fist-sized diamond at, say, $75,000,000 (roughly proportional to the squared ratio of their sizes).

So...yeah. Diamonds have incredible value, and the main reason people think of things like "fist-sized" gems is because Fantasy Authors Have No Sense Of Scale. In our world, good-quality diamonds the size of your thumbnail are worth hundreds of thousands of dollars.

For comparison, a gold piece in 2e (and by implication later editions) is roughly 9 grams of gold, such that there are about 50 gold pieces per (avoirdupois) pound of gold. 9 grams of gold is worth (very) roughly $500. So, if we use 1 gp = $500, a 5000-gp diamond is worth roughly $2,500,000. The baby's-fist-size diamond would be worth, again very roughly, 150,000 gp. The Greater Star of Africa, the single largest high-quality cut diamond extant today, would be worth very roughly 800,000 gp.

As stated, the sense of scale is so completely off, it's hilarious. A 5000 gp diamond, from what I can tell, would be about 10 carats. That's 2.0 grams, or 0.57 cubic centimeters (given its density of 3.51 g/cm^3). For comparison, a Jelly Belly bean is very roughly 2.6 cubic centimeters in volume, so a 5000 gp diamond would be in the ballpark of a quarter of a Jelly Belly bean.

 

[EzekielRaiden]

A quadrillion tons of diamonds lurk deep inside Earth

The sparkly gems are even more common than thought, based on the latest estimates.

www.nationalgeographic.com

I dunno. There are a quadrillion tons of them on Earth.

But the vast majority of those diamonds are completely inaccessible to us even if that model is correct--as that article explicitly says. Most of them lie several miles below the surface, whereas us digging even a single hole half that distance is an incredible achievement of engineering.

 

[Maxperson]

These are my favorite diamonds.

 

[Maxperson]

But the vast majority of those diamonds are completely inaccessible to us even if that model is correct--as that article explicitly says. Most of them lie several miles below the surface, whereas us digging even a single hole half that distance is an incredible achievement of engineering.

Yep, but lots of them get pushed up from the mantle to where we mine them. One mine in one country puts out 30,000 carats weekly. At 30% being gem quality, that's still 9000 carats of gem quality diamonds each and every week. And that amount has been put out by many mines for many years.

 

[Dannyalcatraz]

You can’t compare apples & apples on RW mining vs typical D&D campaign settings. Magic and the creatures that use them skew everything.

Dwarves, earth elementals, Move Earth, Mattock of the Titans, planar gates and Wish, for instance, could make diamonds at least as common as they are in the modern world. Or more so.

Tangent#1 on diamond scarcity: back in the 1990s when Russia was having a severe wheat shortage and South Africa wanted to play hardball to make it more difficult for them to get the loans they needed to buy food on the international market, the Russian government invited 60 Minutes to see some of its diamond vaults. As Mike Wallace (as I recall) wandered around a single vault the size of a small store full of shelves similar to a library’s, his guide led him to one aisle that was where they kept 1ct flawless brilliant cut white diamonds. He then claimed there were several aisles like it in that vault, and dozens of such vaults scattered across Russia. He said that if Russia couldn’t get the loans they needed, they’d start selling diamonds.

South African opposition to Russia’s loans evaporated a few days after the segment aired.

Tangent#2 on diamond scarcity: Dr. Freid, my gemology prof, was among the last group of gemologists ever to see the Persian (modern-day Iran) Crown Jewels intact. His group given 2 weeks to appraise the collection. His few permitted pictures and his personal observations were of 20+ foot tall vaults of unknown depth stacked to the ceiling with gemstones of all major types. Mostly rubies, but everything else as well, including diamonds. Most of it was uncut, but they were still kicking fist size gem materials out of their way to walk. They explained 2 weeks was insufficient time to appraise a “Ritchie Rich” level (his words) collection like this. Iran did not renew their visas. Shortly after their visit, the Iran-Iraq war started, and he believes that a large portion of the Crown Jewels were sold off to fund the war effort. (They apparently have never been seen since that time.)