Below, you can find the full FFXIV: A Realm Reborn item info for the Luminous Crystal item. This item is a Quest Items 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.

Luminous Crystal - Quest Items - Items

Luminous Crystal
Quest Items

Suits: All Classes

Level: 0 		Item Level: 1

NPC: FFXIV Gil 0

A glowing crystal discovered growing inside one of Eorzea's creatures. The source of its luminosity remains unknown.