Single crystals of lunar clinopyroxene containing a second exsolved clinopyroxene have been investigated bystepwise heating experiments combined with X-ray diffraction techniques. Results show that the pigeonite-augite two-phase region narrows with increasing temperature, but is intersected by the solidus. Exsolution lamellaein pyroxenes from lunar basalt 12021 are homogenized into the host pyroxene at a temperature close to that of the solidus for a given pyroxene composition. The earliest pyroxenes in rock 12021 crystallized at ll75°C; pyroxene crystallization continued to approximately 960°C.

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