Black pearls have been found in Mexico’s Gulf of California since the area was settled more than 2,000 years ago. Attempts at culturing pearls in this area have met with varying success over the past century. Today, a pearl farm in Guaymas is producing commercial quantities of mabe as well as bead-nucleated full-round cultured pearls from the indigenous pearl oyster Pteria sterna. This article provides an overview of the history of natural and cultured pearls from Mexico, describes pearl culturing at the Guaymas farm, and focuses on the properties of bead-nucleated cultured pearls from P. sterna. These cultured pearls have a brown or gray to dark gray body color with various interference colors caused by the stacking of platy aragonite crystals and organic matter. One indication of their natural color (and their Mexican provenance) is a red fluorescence to long-wave UV radiation.