From its spectrum this is classified as an S-type asteroid, indicating a stony composition. Photometric observations show a synodic rotation period of 14.206 ± 0.002 hours with a brightness variation of 0.28–0.43 in magnitude. A subsequent study at the Altimira Observatory during 2010 was in agreement with this estimate, yielding a rotation period of 14.208 ± 0.040 hours. Based on a model constructed from the lightcurve, the shape of Koronis resembles that of Ida, although it is a bit larger. 
The asteroid itself may not be spectacular, but the Koronidian family of asteroids named after it is one of the most important. This cluster was created during a collision some 15 million years ago, with 158 Koronis retaining about 98% of the combined mass. One member of the family, 243 Ida, has been visited by spacecraft, and gives some idea of how the other asteroids in the family may look.
^Buchheim, Robert K. (July 2011), "Phase Curves of 158 Koronis and 535 Montague", Bulletin of the Minor Planets Section of the Association of Lunar and Planetary Observers38 (3): 128–130, Bibcode:2011MPBu...38..128B.
^Molnar, Lawrence A.; Haegert, M. J. (September 2009), "Details of Recent Collisions of Asteroids 832 Karin and 158 Koronis", American Astronomical Society, DPS meeting #41, #27.05, Bibcode:2009DPS....41.2705M.