Void Crystal

A Void Crystal is an ingredient for high level enchantments, and some high level crafting items.

Source
Void crystals are obtained through disenchanting.
 * equipment, iLevel 100+: ~0.5%
 * equipment, iLevel 95-100: 50% x1, 50% x2
 * equipment, iLevel 105+: 33% x1, 67% x2

As an ingredient
Void Crystal is used in the following recipes:

Blacksmithing

 * Shadesteel Bracers
 * Shadesteel Girdle
 * Shadesteel Greaves
 * Shadesteel Sabots

Enchanting

 * Void Sphere
 * Void Shatter
 * Surefooted
 * Enchant Ring - Stats
 * Enchant Weapon - Battlemaster
 * Enchant Weapon - Mongoose
 * Enchant Weapon - Soulfrost
 * Enchant Weapon - Sunfire
 * Enchant Weapon - Executioner

Leatherworking

 * Boots of Shackled Souls
 * Bracers of Shackled Souls
 * Greaves of Shackled Souls
 * Waistguard of Shackled Souls
 * Redeemed Soul Cinch
 * Redeemed Soul Legguards
 * Redeemed Soul Moccasins
 * Redeemed Soul Wristguards

Tailoring

 * Night's End
 * Soulguard Bracers
 * Soulguard Girdle
 * Soulguard Leggings
 * Soulguard Slippers