Mariposa (Butterfly) Thundereggs
Nayarit, Mexico
Note: They're often passed as "butterfly" jaspers
due to the coloring in their rhyolite shells.

    "Mariposa" is Spanish for "Butterfly" and that's why you would see either "Mariposa Jasper" or "Butterfly Jasper" referring to the same type of silicified thundereggs passed as jasper. Normally, we would prefer to get the thundereggs with agate cores in them, but in the case of Mariposa Jasper thundereggs, it's reversed where we would prefer solid thundereggs without any agate filled cavities. That's because the solid thundereggs tend to have interesting geometric patterns, and they can have splashes of black, yellow, red, tan, and brown. The opened cavities of any thundereggs tend to contain white to colorless  horizontal banded agates, sometimes with yellow to orange opal layers.

Click on the pictures to see larger and closer-up pictures.
Rough Appearance:  Reddish thunderggs with obvious lava flow bands, sometimes with splashes of yellow, and black.
Most are solid, but some will come with white waterline agates/opal.

Typical horizontal opal & agate bands

Orange bands (not seen often)