graphite corresponds to the ABAB... stacking of graphene layers and is the most stable phase of carbon.

For graphene trilayers, two stable crystallographic

configurations are Bernal (ABA) and rhombohedral (ABC) .In the absence of direct evidence of ABC stacking order in trilayers, ABA stacking order has

generally been presumed in most studies (exfoliated samples), as this structure is believed to be slightly more thermodymically stable than the ABC stacking order.

I agree with the above replies. ABA is the most stable packing (hexagobal graphite), ABC being the rhombohedral form, which is metastable as it has never been isolated so far. ABC only exists as defects in hexagonal graphite, and can be produced by grinding and mechanical stresses in general. AAA is totally unstable.

Alain