In algebraic geometry, the Igusa quartic (also called the CastelnuovoâÂÂRichmond quartic CR<sub>4</sub> or the CastelnuovoâÂÂRichmondâÂÂIgusa quartic) is a quartic hypersurface in 4-dimensional projective space, studied by . It is closely related to the moduli space of genus 2 curves with level 2 structure. It is the dual of the Segre cubic.
It can be given as a codimension 2 variety in P<sup>5</sup> by the equations