DIFFERENTIATION

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Differentiation
Partial melting
TE
Imagine heating chocolate chip cookies, the chocolate will melt first.
Differentiation using Smarties
A P F 15 min
Two packets of Smarties are scattered over a tray which is the magma chamber. Each mineral
is allotted a different colour of Smarty. Students remove each mineral or group of minerals in
turn and place them in a layer at the base of the “magma chamber” They do this either as the
teacher tells them or using a very simple temperature of crystallisation chart for the minerals.
Differentiation using cards
A P or I F 15 min
This activity is to help students learn how the minerals change and how the composition of some
of those minerals change. Students are given a packet containing 80 pieces of coloured card.
Each colour represents a different mineral and changes in mineral composition are shown by
changes in shade. The mineral name and chemical composition is given on each piece of card.
Students scatter these on their desk. The teacher calls out which minerals are crystallising and
sinking to the bottom of the magma chamber. Students take those minerals and place them in a
layer close to them on the desk. Subsequent minerals are placed on top of the first layer.
Differentiation of 100 tons of magma
Pa I F 30 min
Students are given a sheet detailing the tonnage of each mineral that crystallises and sinks to
the bottom of the magma chamber within a given temperature range. They use this information
to draw the magma chamber with the different layers containing different minerals.
Gravity settling
Pa I 1 hour
To calculate the speed of fall of crystals in a basic magma
Students calculate the speed of fall for the 3 minerals using the following densities for the
minerals and magma and the Stokes’ equation.
For basic rocks
Olivine, 3500 kg m^{-3}
augite
3400kg m^{-3}
plagioclase (an) 2700kg m^{-3}.
Basic magma at 1200^{o}C 2600 kg m^{-3}
Viscosity of basic magma at 1200^{o}C is 30 kg s^{-1}m^{-1}
The speed of fall is given by Stokes’ equation.
Velocity = (density of mineral – density of liquid) x g x d^{2}
18 x
Viscosity
g = 9.8m s^{-2}.^{ }d = diameter of grain in metres. The densities are in kg m^{-3 }and the velocity in m s^{-1 }
Viscosity kg s^{-1}m^{-1}
Gravity settling experiment
E P F 30 min per mineral
The speed of fall of olivine, augite and plagioclase is measured in glycerol and then adjustments
are made to calculate the speed of fall in basic magma
Liquid immiscibility
D
Shake a jar containing two immiscible liquids before the demonstration. It appears as a single
fluid but will separate out into two liquids over a few minutes if left to stand. Tesco’s
aromatherapy bath oil works well.
Rhythmic banding
Pa P F 15 min
To show the changes in grain size and mineralogy within one rhythmic band
students work out the average grain size and percentage dark minerals at the top, middle and
bottom in a photo of rhythmic banding.
Crystallisation of olivine
Pa I F 15 min
Students plot the temperature of crystallisation against the percentage of Mg and Fe and then
answer questions on it.
Crystallisation of acid magma
Pa I F 15min
This exercise is to show how the percentage of water in a magma increases as the magma
crystallises. Eventually the percentage of water exceeds its solubility in the magma and free
water is formed which becomes hydrothermal fluid.

Earth Science Activities and Demonstrations