Rare Arcane Spells

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.  

Nonexhaustive List

 

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)