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We present a laboratory study of silicate glasses of astrophysically relevantcompositions including olivines, pyroxenes and melilites. With emphasis on theclassic Si-O stretching feature near 10 microns, we compare infrared spectra ofour new samples with laboratory spectra on ostensibly similar compositions, andalso with synthetic silicate spectral data commonly used in dust modeling.Several different factors affect spectral features including sample chemistry(e.g., polymerization, Mg/Fe ratio, oxidation state and Al-content) anddifferent sample preparation techniques lead to variations in porosity, densityand water content. The convolution of chemical and physical effects makes itdifficult to attribute changes in spectral parameters to any given variable. Itis important that detailed chemical and structural characterization be providedalong with laboratory spectra. In addition to composition and density, wemeasured the glass transition temperatures for the samples which place upperlimits on the formation/processing temperatures of these solids in space.Popular synthetically-generated optical functions do not have spectral featuresthat match any of our glass samples. However, the ~10 microns feature generatedby the synthetic data rarely exactly matches the shape and peak position ofastronomically observed silicate features. Our comparison with the syntheticspectra allows astronomers to determine likely candidates amongst our glasssamples for matching astronomical observations.

Disordered Silicates in Space: a Study of Laboratory Spectra of "Amorphous" Silicates