  Hibonite-pyroxene spherules are an extremely rare kind of refractory
inclusion that show a wide range of exotic isotopic properties despite their
defining similarity and simplicity in morphology and mineralogy. One such,
relatively large (about 120 micron diameter), inclusion has been found in one
of the most pristine meteorites, Allan Hills 77307 (a carbonaceous chondrite of
the Ornans group; Petrologic type 3.03). The inclusion consists of two central
hibonite laths of about 30x15 micron surrounded by Al, Ca-rich pyroxene. The
hibonite laths have uniform composition. The composition of pyroxene
surrounding the hibonite is radially homogenously Al,-Ca rich up to about 50-60
microns which transitions to Mg, -Ti rich at the outer boundary.
Hibonite-pyroxene spherule found in ALHA 77307 shares many similarities with
the other previously found hibonite-pyroxene spherules. A distinguishing
feature of the inclusion in ALHA77307 is the presence of two slivers/ wedges at
the opposite outer edge of the hibonite- pyroxene spherule that consist of
rapidly, poorly crystalized, sub-micron minerals with pristine textures. The
pristine petrography and mineralogy of this inclusion allow discernment of the
expected general trend of formation and alteration amongst hibonite-pyroxene
spherules.
