There's an all-purpose spell called Acashic Record which costs 25 Astral Pearls and is Conjuration-5 (or 4?). Very, very expensive.
Most other spells are Thaumaturgy-2 or Enchantment-2 and reveal sites of a particular magic for 2 gems.
Gem gens are crafted items that generate additional gems. There are two basic gem gen items - clams (for astral pearls) and fever fetishes (for fire), although the fetish bearers get diseased, so you're better of having a dedicated province full of diseased people.