A-type asteroids are relatively uncommon inner-belt asteroids that have a strong, broad 1 µm olivine feature and a very reddish spectrum shortwards of 0.7 µm. They are thought to come from the completely differentiated mantle of an asteroid.
A-type asteroids are so rare that as of 2015 only 17 had been discovered.
References
A-type asteroid Wikipedia(Text) CC BY-SA