Fe-rich pyroxenes from a microdiorite dike, Whangarei, New Zealand Available to Purchase

Pyroxenes in a microdiorite dike near Whangarei, New Zealand, formed during cooling from magmatic temperatures >900 °C to nearly subsolidus temperatures at about 700 °C, with development of Fe-rich compositions between hypersthene and orthoferrosilite, between augite and hedenbergite, and around Fe-rich pigeonite. Orthoferrosilite (Fs₉₂En₄Wo₄) forms partial rims on crystals that contain zoning from Mg-rich to Fe-rich orthopyroxene. Pigeonite, with Fe/(Mg + Fe) >0.70, crystallized on augite and ferroan augite or as separate interstitial grains and is rarely mantled by ferroan amphibole. Textures and compositions indicate that the Fe-enriched minerals were late products, or the latest products, during crystallization of the microdiorite. Fe-rich pigeonite and orthoferrosilite were metastable phases that grew mainly as epitaxial overgrowths on early-stage pyroxenes during rapid cooling near 850-700 °C and 700 °C, respectively.