[DF 8] On Gemstones and Carats

[Stripe]

Honestly, I know nothing about precious gemstones. Not really interested in them other than as treasure for role-playing games. Reading over Dungeon Fantasy 8 -- and I love DF 8! -- I wondered how many carats I should make an astounding, jaw-dropping gem of the size common in cinema and high-fantasy fiction, like the ones found in the hands an eyes of golden idles and such. For example, the statue's eye on the cover of the AD&D Player's Handbook or the red gem Abu tries to steal in Disney's Aladdin.

How many carats would a golf-ball-sized emerald, amethyst, ruby or diamond be? Google tells me golf balls are about 42.67 millimeters in diameter.

How about a truly-fantastic baseball-sized emerald, amethyst, ruby or diamond? Again, Google tells me they are 73–76 millimeters in diameter.

Thanks!

[Diomedes]

Per Wikipedia, a carat is 200mg, and a diamond's density is 3.5 grams per cubic centimeter. your golf ball comes in at 40.7 cc's, so a diamond that size would weigh 142 grams – 710 carats, about 5 ounces avoirdupois.

[vierasmarius]

One carat equals 0.2 grams, so just figure out how much the gemstone weighs and convert to carats. For example, Diamond has a density of around 3.5 grams per cubic centimeter, so a sphere 4.3 cm across (roughly 41.6 cm^3) masses 145 g, hence 725 carats. Clearly, such massive stones are ludicrously rare and valuable; DF8 gives it a price tag of over $21 million.

[Refplace]

As the price was already answered one thing to consider if you really want that size without bank rolling the PCs for life.
That is more then a Kings ransom and likely searching for a buyer would be a significant adventure on its own. Its perfectly reasonable to say no buyer exists in fact. They may chop it down to smaller pieces but would lose a lot of the value and still may have troubles.

[Grouchy Chris]

For comparison, the largest cut diamond in the world is the Golden Jubilee Diamond at 545.67 carats. It had an uncut weight of 755.5 carats.

The largest uncut diamond ever was the Cullinan Diamond, at 3106.75 carats. It was cut into 105 smaller gems.

[Stripe]

Originally Posted by Diomedes

Per Wikipedia, a carat is 200mg, and a diamond's density is 3.5 grams per cubic centimeter. your golf ball comes in at 40.7 cc's, so a diamond that size would weigh 142 grams – 710 carats, about 5 ounces avoirdupois.

Originally Posted by vierasmarius

One carat equals 0.2 grams, so just figure out how much the gemstone weighs and convert to carats. For example, Diamond has a density of around 3.5 grams per cubic centimeter, so a sphere 4.3 cm across (roughly 41.6 cm^3) masses 145 g, hence 725 carats. Clearly, such massive stones are ludicrously rare and valuable; DF8 gives it a price tag of over $21 million.

There's no way I can do that math.

Amethyst has a density of 2.65 g/cm^3. How many carats would a golf-ball-sized one be?

Looks like rubies have the same density as diamonds, so I know that answer.

Originally Posted by Refplace

As the price was already answered one thing to consider if you really want that size without bank rolling the PCs for life.
That is more then a Kings ransom and likely searching for a buyer would be a significant adventure on its own. Its perfectly reasonable to say no buyer exists in fact. They may chop it down to smaller pieces but would lose a lot of the value and still may have troubles.

I centered a whole play-by-post campaign on trying to get rid of a large gem once.

In the end, they sold the priceless, magical gem for something like $1,000 split four ways -- which was a substantial sum less than they agreed to steal it for!

It didn't save them. At least one PC was murdered over it.

[Ulzgoroth]

Originally Posted by Stripe

There's no way I can do that math.

Amethyst has a density of 2.65 g/cm^3. How many carats would a golf-ball-sized one be?

Looks like rubies have the same density as diamonds, so I know that answer.

Diomedes' post included the volume of the golf ball (40.7 cc), which multiplied by the density immediately gives ~108 gram. Or, simply putting "40.7*2.65 gram in carats" into google, you get the conversion to 539.27500 carats.

[Stripe]

Thanks!

....

[vierasmarius]

Originally Posted by Stripe

There's no way I can do that math.

The math itself isn't actually too hard. You just need the formula for a sphere: volume = (4/3) * pi * radius^3. Just plug in the radius in centimeters and it'll give you a volume in cubic centimeters, multiply by density (g/cc) to get grams, then multiply by 5 for carats.

[Peter Knutsen]

Originally Posted by Stripe

There's no way I can do that math.

It's very possible to create a "cheat sheet", using Excel or Calc, for a variety of standard gemstone types and sizes. It's just not something I've gotten around to yet, in part because gemcutting would be anachronistic in my primary setting.