Red Rock is a naturally occurring block in the Mountain Ridge biome added by the ExtrabiomesXL mod. It can be mined, yielding Red Cobblestone. It can be obtained by mining it while using a Silk Touch pickaxe or smelting the red cobblestone in a furnace. It can be crafted into Red Rock Bricks and Red Rock Slabs. Red cobblestone can be mixed with three buckets of water in a shapeless recipe to get four pieces of clay. You will also get the buckets back.
It most likely gained the name "Red Rock" to avoid confusion with Redstone.