Fractional_Crystallization

Fractional Crystallization Charles Darwin in 1844 first suggested the possibility that fractional crystallization playsa role in the formation of igneous rocks. This is the process by which solids, generally crytals, which form from a liquid are prevented from reacting with the liquid. Evidence for Fractional Crystallization 1.Observed changes in bulk composition of liquid, e.g. a single volcanic flow or within a single volcano. 2.Zoning in minerals - most silicate minerals crystallized in igneous systems exhibit evidence of zonation, which reflect changes in composition. 3.Reaction Rims - produced by chemical reaction between crystals and liquid or sudden changes in T and P. e.g. pyroxene rims on olivine result when the liquid containing the olivine becomes saturated with respect to silica as aresult of the growth of olivine. Mg2SiO4 + SiO2 ===> 2MgSiO3 In fractional crystallization the solids are removed or isolated from the liquid, resulting in the remaining or residual liquid having a new composition. e.g. Basalt liquid crystallizes olivine (Mg2SiO4) which is undersaturated with respect to SiO2, causing the initial liquid in to become depleted in Mg and enriched in Si, resulting in less Mg and more Si in the liquid, after forming the olivine. If the olivine is now removed liquid, olivine, crystallization, fractional, been, g/cc, solids, solid, crystal, within, thick, single, si, settling, minerals, mg, interpreted, flow, floatation, evidence, density, convection, composition, changes, chamber, volume, volcanic, top, suggested, sio2, sill, rims, resulting, result, respect