Dark shard amulet

A dark shard amulet was a magical amulet used by warlocks to tap into some of the power of their patrons.

Description
A typical dark shard amulet was made from a fragment of resilient material that originated in the native plane of the warlock's patron.

Powers
While attuned to the amulet and wearing it, a warlock could use it as a spellcasting focus to cast spells. In addition, once per day, the wearer could invoke the power of the amulet to cast any warlock cantrip that was unknown to the caster. Success was not guaranteed, though, as it depended on the warlock's understanding of the arcane forces at work for the amulet to operate.