  The classical theory of differentiation states that due to the heat generated
by the decay of radioactive elements, some asteroids form an iron core, an
olivine-rich mantle, and a crust. The collisional breakup of these
differentiated bodies is expected to lead to exposed mantle fragments, creating
families of newly-formed asteroids. Among these new objects, some are expected
to show an olivine-rich composition in spectroscopic observations. However,
several years of spectrophotometric surveys have led to the conclusion that
olivine-rich asteroids are rare in the asteroid main belt, and no significant
concentration of olivine-rich bodies in any asteroid family has been detected
to date. Using ESA's Gaia DR3 reflectance spectra, we show that the family
(36256) 1999 XT17 presents a prominence of objects that are likely to present
an olivine-rich composition (A-type spectroscopic class). If S-complex
asteroids as the second most prominent spectroscopic class in the family are
real family members, then arguably the 1999 XT17 family has originated from the
break-up of a partially differentiated parent body. Alternatively, if the
S-complex asteroids are interlopers, then the 1999 XT17 family could have
originated from the breakup of an olivine-rich body. This body could have been
part of the mantle of a differentiated planetesimal, which may have broken up
in a different region of the Solar System, and one of its fragments (i.e. the
parent body of the 1999 XT17 family) could have been dynamically implanted in
the main belt.
