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Investigations of reaction mixturesREx(Au0.79Si0.21)100-x(RE = Y and Gd) yielded the compoundsREAu3Si which adopt a new structure type, referred to as GdAu3Sistructure (tP80,P42/mnm,Z= 16,a= 12.8244(6)/12.7702(2) A,andc= 9.0883(8)/9.0456(2) A for GdAu3Si/YAu3Si, respec-tively). REAu3Si was afforded as millimeter-sized faceted crystalspecimens from solution growth employing melts with composi-tion RE18(Au0.79Si0.21)82. In the GdAu3Si structure, the Au and Siatoms are strictly ordered and form a framework built of corner-connected, Si-centered, trigonal prismatic units SiAu6. RE atomsdistribute on 3 crystallographically different sites and each attain a16-atom coordination by 12 Au and 4 Si atoms. These 16-atompolyhedra commonlyfill the space of the unit cell. The physicalproperties of REAu3Si were investigated by heat capacity, electrical resistivity, and magnetometry techniques and are discussed in thelight of theoretical predictions. YAu3Si exhibits superconductivity around 1 K, whereas GdAu3Si shows a complex magnetic ordering,likely related to frustrated antiferromagnets exhibiting chiral spin textures. GdAu3Si-type phases with interesting magnetic andtransport properties may exist in an extended range of ternary RE-Au-Si systems, similar to the compositionally adjacent cubic 1/1approximants RE(Au,Si)