Visual Fractional Crystallization Model. To use this model, use the sliders to select the number of Si, Al, Mg, and Ca atoms in the model magma chamber. (Note that you can click on the slider or drag the handle.) The number of oxygen atoms needed to charge-balance the magma will be calculated for you. Click on the "Set Magma Composition" button and the selected number of atoms should appear in the magma chamber. Click on any of the "Fractionate Minerals" buttons and one formula's worth of the atoms in the selected mineral will be removed from the magma and confined in a rectangular "mineral grain." To see how the chemistry of the magma changes as a mineral is removed by fractional crystallization, continue to click on the "Fractionate Minerals" buttons and follow the changes on the graph. Use the radio buttons to change the oxide axes of the graph.

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