When explaining the nature of magic to Eragon, Brom uses the example of a master who, using the word for water, could create a gemstone, because the connection between water and the stone was clear in their mind (an early clue that magic is somewhat untethered from the Ancient Language, incidentally):

“A true master could just say water and create something totally unrelated, like a gemstone. You wouldn’t be able to understand how he had done it, but the master would have seen the connection between water and the gem and would have used that as the focal point for his power.”


On the other hand, Brom also explains that the universe exacts a toll for using magic: the energy of the user.

He leaned forward, eyes gleaming. “Until then, I will say this to discourage any experiments: magic takes just as much energy as if you used your arms and back. That is why you felt tired after destroying the Urgals. And that is why I was angry. It was a dreadful risk on your part. If the magic had used more energy than was in your body, it would have killed you. You should use magic only for tasks that can’t be accomplished the mundane way.”


Magic can be used to accomplish things that would require manipulations that are physically impossible for a human, elf, dwarf, or Urgal to perform, but the energetic cost of those manipulations must still be paid.

Later books show some ways to circumvent this limit slightly. The energy can be drawn from nearby plants or animals, at the potential cost of their lives. Energy can be stored in receptacles over time. And Tenga might be working on some funky solar-powered magic. But the basic limitations remain: you need an energy source.

The energy cost of creating any decently-sized object from energy is, of course, extraordinary. A tiny 2-carat (0.0004 kilogram) diamond has an energy equivalent to 8.6 kilotons of TNT, half the yield of early atomic bombs. That sort of energy can’t come from the biological processes of a human being, or even hundreds of plants or animals.

How, then, can a magician create a gemstone or other object?

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    It's not clear that mass-energy conversions work the same in that universe. There's also a certain ambiguity: we're not actually shown cases of conjured objects anywhere that I can remember, which would lend a certain credence to the idea that Brom was talking about transmuting something else into a gem, rather than creating one out of nothing. The caster would still be creating one, in the same sense that a sculptor creates a statue or a cook a meal.
    – Darael
    Nov 8, 2016 at 13:03
  • It was mentioned in the last book that a caster once annihilated the matter in his own body to create a huge explosion. If I were in the Eragon universe and I really needed to "conjure" a gem by saying water, I would convert some of the blood in my hand to energy, and channel that energy into creation of a diamond, (water ~ blood -> blood diamonds), or an aquamarine (water = aqua -> aquamarine).
    – Charles_F
    Nov 10, 2016 at 16:42
  • @CharlesFrayne - That's not how things work. A magician uses their own biological energy that they would normally get from their metabolism, or from the metabolism of others. It's not possible to use the radiation one gets from blowing oneself up, any more than it's possible to use solar energy, wind energy, or phonons. Tenga thinks he can use solar energy to get unlimited magical power (reading between the lines), but if even if he ever can figure that out, no one knows that trick as of the books.
    – Adamant
    Nov 10, 2016 at 18:11
  • @Adamant Hmm. I think figuring out that trick is probably the best bet. I don't see why biological energy ought to be different from any other type apart from the lack of a convenient container. Failing that, you might do some experiments conjuring really light crystalline structures. Aerographite, for example, is about 19 million times less dense than diamond, which brings the energy down to about 0.5kg of TNT for a piece the size of a 2-carat diamond, which seems perfectly doable if you've got a decent crowd.
    – Charles_F
    Nov 10, 2016 at 19:39
  • @CharlesFrayne - It's different because magic. ;) The basic rules are mentioned in my question. Physics this is not.
    – Adamant
    Nov 10, 2016 at 20:12

2 Answers 2


I had always assumed he used magic to make a gem out of the water; as is implied in the quote:

“A true master could just say water and create something totally unrelated, like a gemstone. You wouldn’t be able to understand how he had done it, but the master would have seen the connection between water and the gem and would have used that as the focal point for his power.”

It sounds as though he changes the water into a gem. If they had an intuitive understanding of physics, this seems like it would be possible without a mass-energy conversion.

By manipulating the individual sub-atomic particles, the magician could in theory catalyze reactions that create higher and lower elements, to change the oxygen and hydrogen in the water to elements like carbon and metals which could form a crystal lattice.

Depending on how the energy spending system works; the energy required to reorient the atomic structure could be possible. Especially considering some of the reactions could release energy after an energy threshold is reached.

There is also the possibility that nearby mass can be converted to energy to aid in the process; or the magician could even convert some of their own mass to energy. I believe to do this, the magician would have to have some understanding of this conversion process. Perhaps it's just me being optimistic; but it could also be the kind of knowledge a "true master" would have.


I believe that Brom was referencing using materials from the environment around him to form a gemstone, not actually converting energy to mass. Also the magic users clearly have some control over light energy, as I believe bending light was used to make somebody invisible at one point. If they have the ability to bend light, then crystalline structures can be formed much easier according this Princeton study 1 Light can be made to behave as a crystalline solid. This could be the most energy effective way to create a crystal. Also based on scientific knowledge of the time, Brom would not understand that light is a physical thing, so to him it would appear as though a crystal was made from thin air. The master magician may have just bent light and condensed it to a solid using magic. Colors could be made by using the aforementioned water as a prism to seperate the light into different wavelengths. This is how the word water was used to create a gem.

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    The first part is probably right, but the rest is counter to the principles laid out in the books.
    – Adamant
    Dec 28, 2016 at 6:51

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