This skill allows the character to "overwrite" the pattern of a spell stored within a Spellgem with any other spell known by that character. This ability requires 3 Action Points and 10 Magic Points. Weaving a new pattern into a Spellgem will reduce the charges in the gem to 0.
A character cannot learn a spell from a Spellgem that has 0 charges in it, nor can the Spellgem be overwritten. The gem must first be recharged at least once before it can be overwritten or another character can learn the spell.
Triggering the last spell charge stored in a Spellgem normally destroys the gem, however characters with Pattern Weaver have an innate ability to release the last charge without damaging the gem. A character with Pattern Weaver that uses the last charge of a Spellgem will instead have a Spellgem with 0 charges in it. Characters without Pattern Weaver that use the final charge of a Spellgem will still destroy the gem as normal.