Overview
Gemstone A is a material needed to add a Special Ability (SA) to A-grade weapons and to augment them. You obtain it from monster drops at level 60+ or by buying it from other players.
Where to Get It
Gemstone A drops from level 65+ monsters in the Wall of Argos, Forge of the Gods and Imperial Tomb. You can also spoil it (Bounty Hunter) from monsters in the same zones. On low-rate servers, farming Gemstones is a slow grind, so many players prefer to buy them from others. One more source is crystallization of A-grade gear, which returns a small number of Gemstones.
Uses
The main sinks are: adding an SA to an A-grade weapon at the Blacksmith of Mammon (requires 20–30 Gemstone A), and weapon augmentation via Life Stone (requires 20–36 Gemstone A depending on the Life Stone level). It is also used to craft certain A-grade items. Stockpile your Gemstones in advance — a failed augmentation means you will need extra attempts.