Al-rich pyroxenes are either from some high pressure meta-sediments or found as minerals that crystallized in impact melt rocks (the later likely occures after decompression)
Greshake et al. (2010) Brownish inclusions and dark streaks in Libyan Desert Glass: Evidence for high-temperature melting of the target rock. MAPS 45, 973–989.
Additinal references to Al-rich pyroxenes are given in the paper. i.e., Conrad et al. 1988; Carrington and Harley 1995; Montel and Vielzeuf 1997; Bultitude and Green 1967; Montel and Vielzeuf 1997; Hecht et al. 2008;