Heartshard Resonator

The Heartshard Resonator is a thumb-sized violet crystal suspended within a tarnished copper cage. The crystal is faceted like a frozen drop of amethyst blood, yet something soft and warm seems to pulse within it. When held, it gives off gentle heat comparable to a sun-warmed stone. Near concealed doors, secret passages, hollow walls, buried mechanisms, or worked stone of unusual significance, the copper cage begins to vibrate and the crystal produces a barely audible hum. Its surface bears no visible runes, though unfamiliar geometric marks sometimes appear in its facets when exposed to moonlight.