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Quite a few higher-level spells require x GP of gemstone or gemstone dust in order to cast -- I will not bother listing them here, as it'd just take up space in the question.

However, the value of a gem is primarily determined by Cut, Color, and Clarity (or lack of imperfections), not its size. Considering that the same base material can vary widely in these regards from industrial-grade stones that are practically worthless to a jeweler, but still useful for their material properties up to the finest gemstones money can buy, what minimum standards are required of a gem in order to be usable as a spellcasting material component?

Must it be cut before it can be used, or can uncut (raw) gems be used for casting, straight out of the ground? Could a wizard cast a spell that say called for a sapphire or a ruby with a crystalline lump of industrial corundum (synthetic sapphire) instead of a natural gem? Would a large shard of bort be useful for spellcasting in lieu of a gem-grade diamond?

Citations strongly preferred here, by the way -- if you need to dig back into the archives, that's OK, but right now, this is something that I would not even know how to consider from a DM or player perspective.

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    \$\begingroup\$ I doubt this is specifically mentioned anywhere, but even if it is, more detail would lead to better answers, I think. Why do you want to know? Are your PC's going into the mining business? \$\endgroup\$ – SirTechSpec Jul 23 '16 at 3:57
  • \$\begingroup\$ Related: How big is a 50 gp diamond? \$\endgroup\$ – Olorin Jul 25 '16 at 11:23
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You're suffering a misconception.

In the real world, gem size is an extremely important marker of value: the 4th 'C' that you missed, Carat. Unusually large gems are worth exponentially more than smaller ones of comparable quality.

However, in D&D, all gems are measured by a single universal standard: their GP value. No version of D&D has ever gone into the specific qualities of a gem, because very few players would care for that much extra book keeping. Gems are simply abstracted into a condensed form of currency.

It would certainly be possible to extrapolate some system of evaluating gems into the 4 C's, but in the end this will provide a great deal of bookwork, and after all that the players won't care: "Yea, but how much is it worth?"

That level of detail is simply below most players' level of concern. Further, unless you plan to give lessons in gemology, much of it would be meaningless to most players, and you will spend an inordinate amount of time re-explaining how to evaluate the gems. After all that, they're just going to ask again: "Yea, but how much is it worth?"

Gems have 3 basic purposes in D&D.

  • high-density currency, a chest of gems is much smaller than the same value of gold
  • decoration, such as on jewelry or a ceremonial weapon
  • money-sinks, restricting the availability of high-level spells.

Bort is really poor quality Diamond. If such a thing existed in a given D&D world, then it would just be Diamond, and you would still need the same GP value worth of the material.


In 'regular' D&D, there is no way to produce artificial gems or similar items with high intrinsic value (the money metals, for instance).

The typical response would likely be "They aren't real gems, so they don't work."

Some DM's would happily let you try it, and then have fun messing with the outcome of the spell.

In the end it would be up to each DM to make a ruling on artificial gems.


As discussed above, gem qualities are either ignored, or assumed to be of a fairly standard type. Common gems would be assumed to be cut, though likely not expertly. As spell components, this is all largely irrelevant. Again, the only measurement the spell is concerned with is how much the lump of material you are presenting is worth. Absolute value only, you cannot haggle with your Spell. Many spells also do not care if you use one or many gems, as long as the total value is achieved.


I would like to have been able to present citations for all of this, but I have never seen anything in any of the 5 editions (and multiple subsets) of D&D that I have played. This is in relation to both gem quality, and even more so to the idea of artificial gems.

D&D is intended to be a game of fun. For the majority of players, going into this level of detail reduces the game to 'crunch', bogging it down with bookkeeping and trivial details. Very few would find this to be an enjoyable way to play.

My recommendation is that the best way to consider this is to consider it a poor investment of time which will cost you far more enjoyment than it provides.

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  • \$\begingroup\$ If you're wondering why I asked -- a given crystal of gemstone material can be valueless for jewelry purposes, yet still valuable for its intrinsic material properties -- entire wafers of high-purity synthetic sapphire are used in semiconductor work as a surrogate substrate for materials that can't be grown in bulk, for instance. \$\endgroup\$ – Shalvenay Jul 23 '16 at 5:31
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    \$\begingroup\$ Right, but like I said, in D&D, "synthetic gems" are just not a thing. Most, if not all, creation spells are directly banned from outright "printing money", whether it be gems, or precious metals, or whatever. Gems are all naturally formed, and of an approximately standard quality. If you want to roll up a homebrew modern-era world, that would be a different story, but in that case D&D is probably not the appropriate game system to start with. \$\endgroup\$ – tzxAzrael Jul 23 '16 at 6:35
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The only grade required is that is that it be a gem, not merely a rock.

If you would like to introduce lower grades of stone to your game, there's a way to do this with the existing crafting rules (Player's Handbook page 187). You can designate a diamond-in-the-rough as the raw material for crafting a cut diamond, with half the gp value. Add these uncut non-gem quality stones as treasure.

A character proficient with jeweler's tools now enjoys a tangible benefit: they can cut a rough stone into a gem, which is both more valuable and usable as a spell component. For example, to cut a 50 gp diamond suitable for the spell Chromatic Orb would require 10 days of work and raw materials (the rough stone) worth 25 gp. If you want to make things nail-biting, you could even ask for a Dexterity check to see whether they ruin the stone.

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This question is in fact exactly the same as "how big is a 50 gp diamond?", because carat (weight) is directly proportional to a diamonds size, and the carat is most of the value of a diamond. To clarify, here the full formula for a diamonds mass in carat derived from its basic properties, variables first, constants last:

  • \$M=d \times r^2 \times f \times \rho \times \pi \times \frac{1carat}{0.2g}\$

    \$d\$ is the depth of the diamond from table flat to tip, \$r\$ the radius (=\$\frac{\text{diameter}}{2}\$), \$f\$ is the formfactor and is derived from the actual shape: it is \$1\$ for a cylinder, \$\frac{1}{3}\$ for a cone, diamond cuts are, depending on actual shape, very close to a cone (depends on the angle of the table), \$\rho\$ is the density of the stone, for diamonds 3.3-3.35 g/cm³, \$\pi\$ because we assume a round cut, \$\frac{1carat}{0.2g}\$ is the conversion from grams to carat

As you easily see, size and weight (carat) are proportional to each other by a factor of dimensions³ = volume (times density) = mass. The other 3 factors in gem evaluation, cut, clarity and color, do grant some sort of 'base price', but if you ask any diamond trader, he'll tell you that at least half the price of a diamond comes from it's size. The most expensive diamonds are not the most clear, white/blue/pinkish, they are the well cut huge ones:

  • Hope Diamond weighs 45.52 carat and is worth 200-250 million USD while being of a "fancy deep grayish blue", a color that is usually not awarded with that high prices for it does not shine enough. People prefer the less grey finish of sapphires.
  • Golden Eye Diamond weighs 43.51 carat and fetched almost 3 million USD. Which is quite much for a yellow diamond, as most are considdered only industrial grade. If size wouldn't matter, it would have ended in the industry.
  • Allnatt Diamond weighs 101.29 carat and is worth at least 3 million USD. His color is of the very same yellow many industrial diamonds sport. Without the sheer size that is coming in one chunk, you would not fetch anything for this stone: 101 carats of industrial diamonds cost 30-1010 USD, depending on grain size!

By cutting a diamond, up to 70% of its mass get lost. For jewlery size and grade diamonds (that is, something below 10 carat - above it gets wonky), the cut gives about a quarter to third of the value to a diamond, half of it is the weight (carat) and the rest quarter to sixth are color and clarity. That is, unless the color or clarity disqualify a stone to be a jewlery stone, in which case only grain size and weight matter, as you got industrial ware then. Those huge stones mentioned above, however gain aditional value not only from the material properites, but from their stories.

If you find large enough (or just enough low quality) diamonds, those could possibly be used to cast with, but raw stones are worth at best half of the cut ones, often less: fine grade raw diamonds trade for somethign around 2000 USD/carat, the same weight gems in cut fetch prices up to 10 times higher - and raw stones are apprised mainly for color and weight, clarity is of somewhat less concern as it can be apprised wrongly due to the irregular suface.

Industrial grown stones on the other hand are appriced much less than natural stones - you would need an even larger lump of grown corundum than an uncut sapphire of the same worth! Grown stones are cheaper by a Factor 5 to 20, as the Geological Institute of Kiel told me once - even though those stones are better in clarity and color. So there: a cut natural gem is worth more by a factor of 50-200 to a grown (and then cut!) gem.

However, that all does not change one fact: Gems of 50 gp are gems of 50 gp worth. If said gems are a huge bag full of synthetic grown sapphire, a fist sized raw and uncut natural sapphire or some three or 4 small, polished and cut sapphires, they are all "50 gp of sapphire". If you go and buy the pieces for your 50 gp of diamnond from the cheap, throw away pieces that the jewellers don't want, you will need much more of the same stuff to get the same "50 gp of diamonds".


Or to phrase it differently: It is up to the GM what shape said "50 gp of gems" take, as long as those are somewhat logically in themselves. Nowadays stuff not useable for jewelery is worth much less, but it is useable for sawblades and such, giving it still a value. In a world where said 'unwanted' stones are useable for magic, they might even be worth more than today, as there is some demand for them.

If synthetic stones are available at all or how much they are worth or if they are useable for magic in a d&d fantasy setting is GM fiat. If this would be system agnostic, I would point to shadowrun, where synthetic materials have no magical properties, but that is not an answer to the original question.

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  • \$\begingroup\$ Very interesting bit of gemology here, but it still leaves the question unanswered: How does this apply in the game? There is no mention anywhere of how many carats a gem is, nor any hint of a conversion between GP and Carats. \$\endgroup\$ – tzxAzrael Jul 23 '16 at 14:47
  • \$\begingroup\$ Aye, knew I forgot something. Extended and hope to answer the missed parts now. \$\endgroup\$ – Trish Jul 23 '16 at 15:03
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    \$\begingroup\$ Excellent! +1 for all the interesting details. I like the idea of using the "junk gems" for magic, giving them use and value, and the "pretty gems" (eg, those with high clarity and color) for decorative gems. It makes perfect sense, I can even see it in my head right now.. a Jeweler looking at the pile on the table. "Oh very nice, the Baroness has been looking for good sapphires... Ah yes, the Mage's Guild has a big order in for less colorful gems like this one..." \$\endgroup\$ – tzxAzrael Jul 23 '16 at 15:09

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