Psyche is massive enough that its perturbations on other asteroids can be measured, which enables accurate mass and density values. Its density turns out to be extremely low, indicating extreme porousity or (less likely) a non-metallic composition. In other words, the asteroid is probably a gigantic rubble pile. (1) (http://homepage.mac.com/brother_guy/.cv/brother_guy/Public/Asteroid%20Densities.pdf-link.pdf)
Only one stellaroccultation event by Psyche has so far been observed (from Mexico on March 22, 2002). Lightcurve variations indicate a non-spherical body.