EARTH232 Lecture Notes - Lecture 4: Fayalite, Forsterite, Conoscopic Interference Pattern
26 Aug 2016
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Lecture 4: solid-solution series between forsterite and fayalite, orthorhombic orthosilicate with isolated sio4 linked by mg or fe ions, isomorphous: same crystal structure but different elements (ex. Forsterite vs fayalite: * ferrous iron (2+) substitutes into olivine but not ferric iron (3+, stability of igneous minerals during weathering is the reverse of bowen"s rxn series. Olivine, pyroxene least stable and quartz, k-feldspar most stable. Ca-rich less stable than na-rich: mafic magma that erupt onto seafloor consist primarily of olivine and pyroxene which are susceptible to weathering (react with sea water to form for ex. Alteration product of olivine, fluids going through cracks in the mineral propagate into the interior of the mineral. Thus a coupled substitution is used in such a case vs single substitution that can be used: in order for a substitution in plagioclase incorporated into magma to occur a sio bond has to be broken.
