......Hmmmm. Acceptable.

"So to open the gun case maybe one of us should get the ability to feel and move small things. That are close to us. Instead of magic to open locks generally. So it's useful more than once."

"And it'll have to be small things because general telekinesis would be too much?"

"The more limits you put on a thing the less it costs. There's math but I can't really remember much of it. I got kicked out of the bookstore."

"...what parts of the math can you remember?"

"Um, for telekinesis specifically they had some people do different things with it, and did math... Volume... No, distance outside of you is squared... I mean, proportional to the squared... I think that means multiplied twice? Um... Force amount is linear. Duration and recharge are logarithmic but I don't know what a logarithmic is."

"...well, the language magic must be good if it's translating it anyway. Do you remember it for any other things at all?"

"I'm THINKING... I think it said you need about five cubic [inches*] of red to be twice as strong as an average man but only three to lift twice as much. Because you're also lifting yourself... I can't really remember much and I hate it. I wish I could have-"

Stolen that book. Adults HATE stealing, don't mention it. 

"It said that it's smarter for soldiers to get magic that makes them better at using guns than just being strong or tough. Good eyes and steady hands and a power to make the bullets magic. It said... There was a long list of different kinds of powers but I can't remember any of the numbers. You can ask the crystals though. It doesn't actually happen unless you go, yes I definitely want this."

*Not translated

...okay. She picks up a red crystal.

This red crystal is full, it helpfully informs her.

He will go over and poke a red one, too.

"We should write everything down before we actually do it. There's only one chance. There's not much water left but plenty of food. Also the donkey." Said animal has gone to sleep in a corner. It doesn't look too healthy.

"Is there a reason we're trying to get something that will open the guns instead of something that will let us directly kill the thing that used to be a mountain lion?"

"I'm worried it won't be enough. Since it has magic too. It was invisible."

...nod.

"What are the other colors?"

"Red, green, blue... White and black... Orange? Yellow. Purple. I haven't counted these yet."

"No, I mean, what do they do?"

"I don't know, they're rare. Red, green, and blue are the most common. I read that white and black together can let you make magic things. Oh, yellow is healing and purple can give you a pocket dimension."

Are there any of those around or just the common ones?

There's a couple dozen of each primary color, four little white ones and three ones that somehow radiate black, as if black was a color, and one lonely yellow.

...Okay, red jewel. Teekay is good but with the constraints in question maybe what she wants is transmutation, will it sell her that?

It can do transmutation! What kind of transmutation!

The more constraints the better, right? What about - identified elements only, so she'll be able to turn the steel in the lock to oxygen, or get water, which she knows to be H2O, out of the presumable silicon in random rocks, but if the rock doesn't have silicon in it she'll have to guess again. Does that make it cheaper - she only needs about half an inch of range away from her fingertips to get through the lock, maybe less, that and speed.

Making it element-to-element is a good start. Half-an-inch range is also a good start. It'll still be pretty darn slow if she wants to be able to do it continuously. Several minutes for a fingernail-sized patch is the most this red crystal could do.

"You're asking it about kinds of magic now, right?"

"Yes." That's not great. More specific, more specific - what if she affects crystal structures in particular, is that small enough, just nudging molecules into or out of alignment -

That is a LOT more efficient. She could do that fairly quickly with a red crystal, if it's not going to be rearranging ionic or subatomic bonds, nearly as fast as she could swipe a finger over things.