To unlock this achievement, you MUST have the Nova Orb, a 15 MP spell that destroys cracked rocky walls. The orb is obtained during some story dialogue in Indigo Forest and can't be missed.
Rocky (the funny-looking rock) is located in a cave in Desert Tail. Make your way to the massive open area in the desert.
There's a teleport pad hidden under a barrel in the middle of the open area. Destroy all barrels and bushes you see to make things simple. Step on the teleport pad.
Once teleported, make your way to the cave just to the right, and go inside.
There, you will find Rocky. Annihilate the poor thing with the Nova spell, and it should drop its aura. Get your button mashing skills ready, and analyze the aura by mashing the A button constantly.
The data of Rocky will be sent to the museum and the achievement will pop :)