Strong Arm is an essence gem which grants a large bonus to Intimidation while imposing a moderate penalty to the other two conversation skills. It is a counterpart to Divine Radiance and Sixth Sense, which provide equivalent boosts for Charm and Intuition, respectively.
In-game description: "Protector Lo Wan was an enforcer for an openly secret society that offered protection to merchants and citizens throughout the Empire. In return for regular payments, the surprising number of accidents that occurred were greatly reduced. Coincidentally, these accidents often occurred in the presence of Protector Lo Wan, and he became very persuasive in getting more business for his organization. As his star rose, so did his tastes. His penchant for gaudy jewelry eventually led to his acquiring this gem, and, at the time of his death at the hands of a crowd of angry merchants, some of his skill was imprinted in it."