Wizards learn their spells from books and teachers built from centuries of prior accumulated knowledge. Sorcerers and some warlocks can spontaneously "Eureka" spells into their knowledge, but 99.9% of the time, they will Eureka a spell that has been used many times before.
In a metaphysical sense, "common spells" and "rare spells" are the same. Rare spells just happen to be spells that most mages, even learned mages who formally study Spellcraft, have not heard of. Rare spells tend to be very old or very new.
If a mage invents a new spell. That spell is by definition a "rare" spell Technically it's a unique spell. If a mage invents a new spell and teaches it to her apprentices, and they teach their apprentices, it will remain a "rare" spell until the new spell becomes widely circulated. Even if a spell circulates for centuries, it can remain a rare spell if it covers a very specific niche that few mages are interested in.
In a lot of cases "new" spells are not literally new. It is very common for mages in different regions and era to unknowingly and independently invent the same spell.
Enchantment
Third Circle
Fast Charge: Like Fast Movement but affects a group.
Improved Waterwalking: Let's a subject walk (or run) on water for an extended period of time.
FIfth Circle
Perfect Day: Area spell locks an area in a specific climate for a long period of time.
Illusion
Mighty Aura spell (2nd circle illusion)
Chameleon Cloak (2nd circle Illusion)
Greater Chameleon Cloak (3rd circle illusion)
Necromancy
bone shaping (3rd circle Necromancy)
Ghostly Invitation (3rd circle Necromancy)
Transmutation
bone shaping (3rd circle Transmutation)
Rare Abjuration Spells
First Circle Spells
Insect Ward: Area spell wards off insects, a proto version of Kitchen Ward
Rodent Ward: Area spell wards off rodents, a proto version of Kitchen Ward
Moisture Ward: Area spell wards off water, a proto version of Kitchen Ward
Third Circle Spells
Corpse Strings: The caster can see a mystical trail connecting an undead to the necromancer empowering it (if there is one). The mystical trails lingers a little bit after the undead creature or necromancer dies or if the undead is released from control or put in "prime" mode, but it doesn't last long.
Fifth Circle Spells
Brutal Grounding: Spell negates flying spells
and negates Feather Fall spells.
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