there are 2 types of crystal (both from cash shop)
1 of them is the one you can earn by paying real money,
This one looks like a llight blue crystals
the other is used by the developers to rewards players (mostly from events) and this second one is bound to your character to prevent people from parrticipating in single event with multiple characters.
(if this wouldn't exist people would make new chars to earn the event rewards multiple times so they could send them to their main char)
This crystal has a purple color (they're also called premium crystals)
You can exchange the normal crystals for premium crystal, so that when you would be able to spend your remaining (just an example

3 crystals (when you earned let's say 1500 and you spent 1497 on something that costs this weird amount of crystals :p )
There are some restrictions to the normal/premium crystals: some items can only be bought with only 1 of them.
So yeah if you buy crystal chips with the normal crystals, you should be able to sell those runes.
PS:
- The 120 crystals you get at level 14 (at least for leaugue chars, I know it's earlier if you're priden, no idea for imperial side) are also bound so if you use these you will make
those runes bound as well
- Lastly equipping runes makes them bound as well so when you're upgrading runes and you don't want them to be bound make sure you don't use a single rune that has already been equipped cuase it will all runes that have used that one bound as well
- Sorry for the long post but I hope it helps