These were initially labeled X-type asteroids, then type DM (dark M) or PM (pseudo-M), before acquiring their own unique classification as P-type asteroids (where the P indicates "pseudo-M").
Niitä ensin sanottiin X-tyypin asteroidiksi, sitten DM-tyyppi (dark M) tai PM (pseudo-m), ennen kuin ne sai oman ainutlaatuisen luokan, P-tyyppi (jossa P ilmaisee "pseudo-m").