A new family of transition-metal-containing phosphates ANa3M7(PO4)6, where A = K, Rb, Cs and M = Mn, Fe, Co, was synthesized via high-temperature (650-800 °C), solid state reactions. Sizable single crystals up to 1 cm (ca. 160 mg) were grown for structure and property characterization. The extended structure comprises of alternating corner- and edge-sharing triangular chains of FeOn (n = 5,6) polyhedra involving four crystallographically distinct Fe(II) cations. The triangular chains propagate along the a and b directions to form slabs, which are interlinked by P5+ and a fifth Fe2+ cation to form the three-dimensional lattice. The magnetic susceptibility studies suggest that some of these fascinating compounds exhibit a ferromagnetic transition at temperatures between 10K and 15K. The field-dependent studies on the oriented single crystal of RbNa3M7(PO4)6 show the occurrence of magnetization steps at 2 -5K. In this report, we will first discuss some prior research developments relevant to the study of geometrically frustrated magnetic (GFM) interactions, followed by the results of our exploratory synthesis in the pseuo-quaternary iron(II) phosphate system and finally some initial investigations of temperature- and field-dependent magnetic properties.