The Ambrosium Shard is an item added by Aether II.
It can be obtained by mining Ambrosium Ore, which is found abundantly in the Aether. It can also be obtained by using Holystone tools, which have a chance to drop an Ambrosium Shard when used. Their primary usage is for enchanting items on the Altar. Shards can be used on Altars by right-clicking on the latter.