Is increase crit chance on jewel, passive tree, gear, etc global?

Is it global or is it specific to a spell.

ie: say I have a jewel that says "increase 10% crit chance", and I have spark and fireball. will it increase crit for both?

Not exactly understanding your example, because you listed two spells, in which case most mods that apply to one will apply to the other or it will apply to neither. There will be some differences, like fire and lightning, but crit is going to apply to both those examples.

A jewel will be global, though I I don't think that exact wording "increase 10% crit chance", is used in the game, and jewels have a specific mod pool that can roll on them. A mod with "10% increased critical strike chance" would apply to anything that can crit. If it has more specific wording attached, like "spell", "melee", "elemental skill" etc, then it will only apply to that source.

Local and global modifiers are a bit tricky, but basically the rule of thumb as I'm aware, is if it is attached to the thing that has the property, it is local. If not it is global. So increased critical strike chance on a weapon, will increase the base crit chance on the weapon, while on a jewel will be global.

There is a more in-depth description of global/local on the page that will explain it more accurately than I do. It can be complex and unintuitive for some mods and niche cases though.
https://www.poewiki.net/wiki/Modifier

POB is a good tool for testing interactions that you are not sure of. It is usually very accurate, particularly with basic mechanics.