Below, you can find the full FFXIV: Heavensward item info for the Soul of the Weaver item. This item is a Soul Crystal and is usually a crafting material or the product of a craft. Sometimes it can be dropped from a monster or found in a chest.

Soul of the Weaver - Amulets - Items

Soul of the Weaver
Soul Crystal

WVR

Level: 55 		Item Level: 136

NPC: FFXIV Gil 0

Upon the back of this crystal plaque are engraved the myriad creations of weavers from eras past.