Abstract: An atmospheric burner assembly for a gas log fireplace comprises a mixing chamber adapted to receive gas from a gas supply and mix gas and air therein. The burner assembly also comprises a manifold adapted to receive gas from a gas supply. The burner assembly also has a burner with a first port communicating with the mixing chamber and a second port communicating with the manifold. The second port is adapted to generate a flame pattern that is embedded within the first port. When installed in the fireplace, the burner assembly combusts pure gas at the second port for rich combustion and a mixture of gas and air at the first port for lean combustion, thereby promoting stage combustion at the burner assembly and producing a yellow chemiluminescent flame.