Organic molecular crystal structures have densities that are typically in the range 1.2-1.4 gcm-3 although these can be increased, in general, to ca. 2.0 GPa through application of pressure. However, the organic heterocycle alloxan is an anomaly, measuring 1.962 gcm-3 at ambient conditions. Compression of an already-dense material gives us a ‘head-start’, enabling us to explore a high-density region of phase space that would otherwise require improvements in pressure equipment for ‘typical’ organics. We will observe the compression mechanism of alloxan, up to 10 GPa, and quantify the strengths of its intermolecular interactions, as it experiences abnormally high densities, in the context of organic structures. Alloxan also undergoes a transition from P41212 to P212121 at 35 K and we will aim to see whether this transition can also be induced via pressure.