Lapis Lazuli Ore is a material block added by vanilla Minecraft. It appears fairly commonly in Caves, but like other ores in Hexxit it can be found well above ground too. A Stone pick or stronger is needed to mine Lapis Lazuli Ore.
When mined, this ore drops 4-8 Lapis Lazuli, possibly more if your pickaxe is enchanted with Fortune. When mined with Silk Touch you get the ore as a block, which you can place or smelt in a Furnace for one Lapis Lazuli. (Not practical)