The Blue Gem's purpose was to open the gate to Raccoon City Hall. On the last fortnight of the Raccoon City Destruction Incident, it was stolen along with several other Gems. It was found in the body of a Restaurant owner.
The Gem was kept in the evidence locker until eventually retrieved by Jill Valentine on the 28th of September. Before checking, the name of the item is Blue Gem. After exploring, the name is Sapphire.