I've been working on a "hands-on" student activity where they can see how molten rock can form igneous rocks of varying composition (fractionation/differentiation). Using M&M type candies in a plastic bag (representing the magma chamber), specific color pairs represent "minerals." Placing them on the plate represents crystallization. The rules of the game only allow certain color pairs to be formed with each step (crudely representing Bowen's Reaction Series).
M&M "magma chambers" ready for students to use.
I'm drafting revised instructions with illustrations to help explain the activity.
By tracking the type and number of M&Ms with each step, students can see how "Incompatible" elements increase in concentration.
My preliminary test with lab last week managed to produce a decent negative correlation between "Mafic"and "Felsic" constituents in the remaining magma.