Found as creature loot drops, casting certain spells on these stores the spell for later use.
Three versions exist. ‘Level’ refers to innate level of a spell. For example Heal is available as a 5th level spell to healing domain clerics, but its innate level is 6 so it can NOT be stored in any crystal.
Crystals accept only ‘defensive’ spells eg buffs and cures. Protection from Alignment, Ultravision, attribute buffs, Death Ward, Freedom of Movement, Spell Resistance, Remove Fear, Lesser Restoration, Remove Curse, Remove Disease, Divine Favor, Magic Weapon, Blade Thirst, and the Cure Wounds series of spells are all fine. Dispel from a crystal targets the person using it.
Direct Damage spells and anything which has a negative effect on your opponents will not be accepted, eg Firebrand or Battletide. Raise dead can’t be stored either.
When a spell which requires components is put into a crystal, the components aren't consumed until the crystal is used. Thus, when you buy a Stoneskin Spell Crystal from someone, make sure you have your diamond powder with you so that when you go to use the crystal it isn’t wasted.
When you attempt to use a crystal while silenced, the crystal is consumed and you get a message saying that it could not be activated due to your inability to use verbal components. It’s a result of the "Use Unique Power" entry in the spells.2da file requiring a verbal component. Just think of it as an activation word.
All spells cast into a spell crystal of any sort are set at caster level 10 for effect and duration. This is their default value and there’s no way to correct this since the "caster level" feature in NWN scripting is quite busted. This means that a level 1 sorcerer or a level 15 sorcerer can both give you a mage armor spell in a spellcrystal that lasts for 10 IG hours.
Do NOT store empty crystals in bags or boxes. If they’re in one over a reset when you go to charge it you’ll get the message "Spell level too high" while trying to store a perfectly level –appropriate spell. This means that the crystal is broken. You may be able to get a DM to swap your broken crystal for a new one. You can have them into a PS, as long as they're sitting loose it will be fine. If they are already charged with a spell, it's no problem having them in containers either.