Evidence has been presented for a density-driven phase transition occurring between supercooled liquids in the system Y2O3-Al2O3. The high- and low-density liquids were quenched to metastably coexisting glasses. Chemical analysis showed the compositions of the two glasses to be identical, and it was inferred that they differed in their densities and entropies. The entropy difference has been verified by calorimetry. Here, we confirm that the chemical compositions of the glassy materials derived from the high- and low-temperature liquids are identical. We present a direct density determination of the two. glasses using sink-float techniques. The measured densities are 3.72(3) g/cm(3) for the glass derived from the high-temperature liquid (i.e., the high-density amorphous or HDA polyamorph), and 3.58(1) g/cm(3) for the low-temperature (low-density, LDA) polyamorph. (C) 2007 Elsevier B.V. All rights reserved.