As of 1.8, Lapis is a required part of Enchanting in Minecraft
In order to enchant, the player needs an Enchantment Table, several Experience Points and the item they wish to enchant. As of 1.8 The Bountiful Update, Lapis Lazuli is required as well.
Note: this is the Lapis Lazuli Item, not the ore, or the block.
Additionally, you also require a minimum of 15 bookshelves, placed 1 block away from the Enchanting Table, to gain access to the tier 3 enchantments. If you do not have 15 bookshelves, you cannot enchant your equipment with tier 3, regardless of how much experience you have, or how much Lapis.
Finally, you need at least 30 levels of experience, to gain access to tier 3 enchantments. Successfully enchanting an item will cost experience, and could drop you below level 30, which will lock out access until you once again gain more experience.
So, to recap: To access tier 3 enchantments in the enchanting table, you need a minimum of
- 15 bookshelves, placed 1 block away from the enchanting table
- 3 Lapis
- 30 levels of experience
If you do not meet all 3 of these requirements, you cannot access tier 3 enchantments.