Rock Pikmin are a species of Pikmin featured in Pikmin 3. They resemble small polished rocks with Pikmin eyes, limbs, and, just like the Winged Pikmin, lavender flowers. The main part of their body seems to be a grey texture of graphite that reflects light, while the 'skin' on their arms and legs appears to be smooth and gray. When Rock Pikmin are dismissed, their sprouts glow gray. Their ghosts are also shaped like small gray rocks with eyes. Just like all other types of Pikmin in Pikmin 3, Rock Pikmin share an Onion and are reproduced through collecting nutrients from Pellets and corpses of dead foes.

Rock Pikmin are the second type of Pikmin Alph discovers in Pikmin 3, the first being Red Pikmin.

Source: http://pikmin.wikia.com/wiki/Rock_Pikmin