Solid solutions of the type Fe 1- xMxBO 3 have been prepared where M = Mn, Cr, Al, Ga, or In. For M = In, Ga, or Cr, x can vary from 0 to 1.0, but the solid solution range is more restricted for M = Al (O ≤ x ≤ 0.32) and Mn (O ≤ x ≤ 0.10). The present investigation of these materials includes their crystal chemistry, thermal stability, and magnetic properties. The calcite-type unit-cell parameters follow closely Vegard's Law. DTA results indicate that the thermal stability increases with increasing M content for M = Cr, Al, or In. Room-temperature magnetic measurements show that the Fe 1- xMxBO 3 phases remain canted antiferromagnets up to the 20 to 30% substitution level, with monotonic decrease in the magnetization and Curie temperature as a function of the concentration of M (dilution effect). Low-temperature magnetic studies of the systems Fe 1- xCr xBO 3 and Fe 1- xIn xBO 3 show anomalous magnetic behavior at the higher Cr and In concentrations.