We report the matrix-mediated mineralization of Na-3(CO3HCO3).2H(2)O at the air interface of NaOH-containing poly(gamma-aminopropyl triethoxysilane) matrixes, which are exposed to a warm and humid mixture of CO2 and air (-37 degreesC; relative humidity (RH) similar to100%; CO2 similar to40 000 ppm) for <10 s followed by extended exposure to ambient conditions with RH in the range 50-60%. Scanning electron microscopy, atomic force microscopy, and optical microscopy are used to characterize the surface and topology, and energy-dispersive X-ray spectrometry and powder X-ray diffraction are used to determine the chemical composition and crystal structure. These results enable us to elucidate fundamental aspects of the mineralization process.