God's instructions for tabernacle worship included a specialized incense recipe, one component being this mysterious substance. Traditional identification points to onycha—the 'fingernail' or operculum of certain mollusks, which when burned produces a pungent aromatic smoke. Ancient Near Eastern perfumery employed various exotic materials, and shell-derived aromatics were valued. The Hebrew name may relate to a root for blackness, perhaps describing the darkened state of the processed operculum. Incense-making was both science and sacred art.