"Sweet Potato Agates" are agates in lithophysae ("Thundereggs") from the State Cihuahua. They have a brownish red skin and show usually not parallel-banded chalcedony (so-called "cloud agate") inside of the lithophysae. They are similar tothe “ small thundereggs from Northern Chihuahua”, are however slightly larger (up to 10 cm in diameter). Their location is not known. The fact that agates are compared with potatoes, makes it difficult to identify this material. The label is understandable and obvious - digging agates from the ground, its shape is similar to potatoes - however, this not unique name is very confusing. in the comparison . We find this designation for agates from Idaho (the "potato country"), for agates from England, even in Chihuahua itself exists a second variety of potatoe agates besides the one described here.