Purple "Pimpleback" Shell 8x16mm Faceted Rectangle Bead - 15-16 Inch Stone Type_Druzy Agate The inner layer of the

The inner layer of the shell is composed of nacre (mother-of-pearl)

It is a potent combination of these minerals

while replicas are often cut or drilled

Ethiopian Opal typically occurs in brown

Purple "Pimpleback" Shell 8x16mm Faceted Rectangle Bead - 15-16 Inch Stone Type_Druzy Agate The inner layer of theA "pimpleback" is a freshwater mussel (Cyclonaias pustulosa) common in North American rivers, characterized by a thick, yellow brown to brown shell covered in bumps (pustules). While not typically purple, the inner lining (nacre) can be iridescent, and related species in the pimpleback complex are sometimes found in Texas waters.