Caption: FIGURE 4: The XRD patterns of spondyle clay (a) and MCSd-7 (b): F, augite Ca(Mg, Fe, Al)[[(Si, Al).sub.2][O.sub.6]]; G, pigeonite
(Ca, Mg, Fe)(Mg, Fe)[Si.sub.2][O.sub.6]; C, quartz Si[O.sub.2]; M, magnetite [Fe.sub.3][O.sub.4].
Ca-poor pyroxene is inverted pigeonite
. Weakly serpentinized olivine ([Fa.sub.35-44]) is more idiomorphic in gabbros than in anorthosites.
or Contain a low-Ca-pyroxene orthopyroxene) absent.
Various factors, including magma composition, control whether orthopyroxene or pigeonite
occurs as the low-Ca pyroxene, but high temperatures yield orthopyroxene and low-pressure crystallization favours pigeonite
Petrographically, the basalts are described as containing calcic plagioclase, augite, and rarer pigeonite
and bronzite, and Fe-Ti oxides, and vary from holocrystalline to variably vitrophyric ([less than or equal to]30%).