How can we determine the cost of ruby dust?

There are spells like Continual Flame which require ruby dust as a material component. The rules explicitly require "ruby dust worth X gp", not "ruby dust made from rubies worth X gp".

Let's say we found a ruby that costs 500 gp and want to crush it to a ruby dust. How much would this dust cost? "500 gp" doesn't seem plausible, since 500 gp worth of dust could be produced from much cheaper rubies of the same total weight.

Related: What is a 500gp Ruby useful for?

• – V2Blast Jun 18 at 21:57

It's up to the DM.

Having said that, D&D pricing doesn't make economic sense, so the answer I prefer1 when I DM is that is you get 500gp worth of dust out of 500gp worth of rubies.

The game also doesn't specify any other properties than value when it talks about most gems. Maybe the price is exactly proportional to weight, i.e. a 500gp ruby is equal in weight to 10 50gp rubies.

1. Mainly for the simplicity
• This is how I have always ruled it. Easy to remember, works well and most players aren't jewellers who are going to tell you how unrealistic it may or may not be. – SeriousBri Jun 18 at 12:37
• @SeriousBri: I hope it would be a very small subset of jewellers who would actually complain about the unrealism, rather than just notice it and accept it as a one of many good simplifications that D&D makes vs. how the world really works. (Or maybe dust from a really nice ruby actually does go farther for spellcasting uses? That's one way to paper over this world-building issue.) – Peter Cordes Jun 19 at 22:46
• I'm not arguing with the things being said, but for the sake of fairness, the question is not "who is responsible for determining the cost", neither "does this make economic sense". The question is "How to determine the cost". If the answer is "just use the cost of the base material", you could say this in a clearer way. – enkryptor Jun 20 at 10:07
• Re "Maybe the price is exactly proportional to weight", In a world where ruby dust is very useful, this could very well be true or close to true. – ikegami Jun 20 at 21:14

Pricing in DnD is largely just a mechanic to restrict access

The 500gp is the barrier, not the mechanics by which the item is gained. Either the item is given as a reward for a task done and worth 500gp or the item is bought with 500gp worth of gold earned. Either way the DM has a method by which to reward the characters with something which opens up more spells.

When you break down the economics or the price requirement on spells you can clearly see this doesn't stack up. If you're in a region where prices are higher because a lack of supply or lower because of over supply that doesn't mean you start having to factor in inflation, production methods or supply routes to calculate the "worth" of a ruby. All the game is interested in is "did the player have to part with 500gp to get this item?"

That being said the final say always sits with your DM - ask them.

• Relatedly: What makes a spellcasting component worth x gp? (though the answers there rather disagree with this one.) – Carcer Jun 18 at 17:11
• Yep, this is part one of the most blatantly illogical narrative aspects of D&D, the grand illusion that there is a unified, single market economy throughout the game world. – Austin Hemmelgarn Jun 18 at 18:55

Unless your GM rules otherwise, you can use a real world analogy to crushed ruby, diamond powder.

Diamond powder of an appropriate grain size (around 50 microns) burns with a shower of sparks after ignition from a flame. Consequently, pyrotechnic compositions based on synthetic diamond powder can be prepared.

If you do want some effect from crushing gems in your game, you can apply some arguments below

The dust costs less

This quora post implies that a 1kg or 5000ct diamond costs $16,250,000.00. Natural Diamond powder seems to cost$2/ct, so equating the two means 5000ct of natural diamond dust costs \$10,000.

That's a price drop of 1/1,625 for crushing gems into dust*.

So your 500gp ruby is now 500/1625 gp or 0.3gp. That's the equivalent of 3sp if 1gp is 10sp.

So in the real world the price really gets crushed.

The dust costs more

In the real world however, you can't use gem powder to cast spells, so the above argument won't necessarily hold true. It's down to the GM to decide if this is the case, that the labour in crushing gems increases the value in the same way purifying raw materials like iron ore into steel increases the value of the product.

It costs the same

It may be that your GM is not swayed by either argument, especially as it relies on real world analogies, or trying to understand D&D/fantasy economies. The simplest solution is to have the two cost the same, either by GM fiat, or some balancing of the above two arguments.

*Note, that it's possible that diamond dust has more utility than ruby dust. Or less.

It's quite likely these arguments about how economics work in D&D are unconvincing, largely because the economy in D&D doesn't make much sense if you look too closely, and even if it did there are too many differences to make proper analogies.

• The problem with using real-world prices is that 500gp of gem dust would probably be more than the average person could carry. – user56480 Jun 19 at 8:37
• Actually, the bigger the diamond the greater the price per weight, so it would be much much less if made from a single diamond. – DonQuiKong Jun 19 at 17:39