LogFAQs > #967870417

Because postgame grinding. It's an extremely powerful gem, so it makes some amount of sense to have it be hard to get. If you set up your gem crafting right, you should only need 4 copies of the crystal to outfit the entire active party and 8 copies to give one to everyone (which is convenient but not necessary), and those crystals can also give Double Attack (which you should have 3-4 copies of) and Unbeatable (which is good to put on everyone), so it's fairly productive farming. If you save scum the chest dropped by the unique version (Magnificent Digalus), you'll get enough of all three gems pretty quickly.