Abstract
AbstractMany important pyroxene minerals undergo subsolidus reactions during their formation process between ∼ 700°C and ∼ 1200°C. The nature of these reactions depends on chemical composition, temperature and pressure. As a reaction result various microtextures may be observed by transmission electron microscopy. These include stacking sequence faults, twinning and antiphase domains which may be related to structural phase transitions.—Exsolution in clinopyroxenes produces lamellae of Ca‐rich (augite) and Ca‐poor (pigeonite) pyroxenes parallel to (100) and (001). The exsolution may result from fluctuations in chemical composition (spinodal decomposition) or from nucleation and growth. The appearance of the final lamellae does not reflect the original process.—Direct in‐situ heating experiments give some indication for the subsolidus reactions. By precession photographs a simultaneous occurrence of lamellae parallel to (001) and (100) is observed. Attempts are made to classify the observations, determine a time‐temperature‐transformation (TTT)‐diagram, and to correlate the observed microstructure with the thermal history of the mineral. The experiments described were carried out on synthetic samples with known cooling rates.
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