For 10 points each, answer the following about oxygen fugacity’s use as a petrological parameter.
[10e] Oxygen fugacity was introduced in the study of mineral syntheses that used redox buffers, such as the system of fayalite, magnetite, and this mineral. This silicate mineral usually exists as a network of SiO4 tetrahedra.
ANSWER: quartz
[10h] This type of magma has a low oxygen fugacity, and thus a low Fe3+ (“F-E-three-plus”) to Fe2+ (“F-E-two-plus”) ratio. Unlike calc-alkaline magmas, this type of magma traces out a concave-down curve towards the alkali corner of an AFM diagram.
ANSWER: tholeiitic (“thoh-lee-IT-ick”) magma
[10m] When this element is present, the relationship between oxygen fugacity and the Fe3+/Fe2+ ratio may not be straightforward because it substitutes for iron in silicate minerals. Forsterite is the olivine end-member that is rich in this element.
ANSWER: magnesium [or Mg]
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