Eight silicate unit vibrational modes were identified in a suite of PbO-SiO2 glasses using micro-reflectance Fourier Transform infrared (μR-FTIR) spectra that were transformed using the Kramers-Kronig relation. The transformed FTIR spectra, in the 800–1200 cm−1 range, were deconvolved systematically into eight Voigt-shaped bands at centers that were predicted from the second derivative of the spectra. The area of the eight bands varied as a function of SiO2 content, and these trends were combined with theoretical constraints to identify and assign the bands to seven provisional silicate units: SiO4−4 (830 and 860 cm−1), Si2O6−7 (900 cm−1), Si6O12−18 (950 cm−1), Si2O4−6 (980 cm−1), Si4O6−11 (1010 cm−1), Si2O2−5 (1050 cm−1), and SiO2 (1100 cm−1). The provisional units were then grouped according to their NBO/T values: NBO/T = 4 (SiO4−4), NBO/T = 3 (Si2O6−7 ), NBO/T = 2 (Si6O12−18 and Si2O4−6 ), NBO/T = 1 (Si4O6−11 and Si2O2−5 ) and NBO/T = 0 (SiO2). The derived quantities of each NBO/T unit compare favorably with nuclear magnetic resonance data for PbO-SiO2 glasses reported in the literature. This new approach for determining glass structure is advantageous because it may be performed on small Fe-bearing samples with minimal preparation, and analyses are rapid and relatively inexpensive.