The group which includes CoS2, NiS2, and FeS2 forms an isostructural series following the pyrite lattice. Heretofore, the formation of the artificial end members of the series has been established, but approximations to CoS2 and NiS2 have not been found in nature. At the Shinkolobwe mine in the Belgian Congo, CoS2 having a pyrite structure is now known. To this mineral is assigned the name cattierite. Material approaching NiS2 is composition and having a pyrite type of lattice has been found in the Kasompi mine of the Belgian Congo. This mineral is tentatively called vaesite. The lattice constants for the natural end members of the series in angstroms are pyrite 5.40667 ± .00007, vaesite 5.66787± .00008, and cattierite 5.52346 ±.00048. The minerals are named after important contributors to the mineral development of the Belgian Congo. The four members of the pyrite series would be vaesite, cattierite, bravoite, and pyrite.