teacher’s notes
student’s notes
Activity 1
Apparatus
Each student (or group) will need
Shallow transparent dish (a plastic Petri dish is ideal)
100 cm
3
beaker
Bunsen burner, tripod, gauze and heatproof mat
Cloth for handling the hot beaker
Chemicals
Each student (or group) will need
1 raw egg white
Salt (sodium chloride)
The teacher will need
Samples of different types of metamorphic rock, for example marble or
quartzite. Suitable lumps can be obtained from a geological supplier.
Click here for details of some suppliers
http://www.earthscienceeducation.com/suppliers.
Safety notes
Care is needed when lifting the beaker of boiling water from the tripod.
It is the responsibility of the teacher to carry out an appropriate risk
assessment.
The activity
Place the white of an egg in a Petri dish. Place about 50 cm
3
of water in a
beaker and add two or three spatulas-full of salt to the water (to increase the
boiling point) and bring the water to the boil.
When the water is boiling, carefully take the beaker off the tripod and place it in
the centre of the egg white on the Petri dish as shown in Figure 1. Leave for 10
minutes and observe again. You should be able to see that a thin layer of egg
white in contact with the beaker has ‘cooked’ and changed texture, ie it has
become white and rubbery.
Extension activity
Students can simulate the deformation of fossils themselves if they have the
Word™ document of the student’s material running on a computer. They just
click on Figure 2A to select it and a series of small circles will appear around
the image of the fossil. They can then ‘squeeze’ the fossil by clicking on one of
the circles in the middle of the left, right top or bottom sides of the diagram and
dragging it to resize the image.
Answers to questions
Q 1. The dictionary definition of metamorphism is a change of form.
Q 2. No – you can’t ‘uncook’ an egg.
Q 3. No – by analogy with the answer to 2.
Q 4. The fossils would have been even more distorted, perhaps to the point
of being completely destroyed. (Further distortion might have been
caused by recrystallisation of the rock but students would be unlikely to
come up with this unless it had been discussed in class.)
Q 5. a) (i) The forces acted downwards from the top of the paper and
upwards from the bottom
(ii)The trilobite has been distorted by about 15-20%.
b
)
(i) The forces acted leftwards from the right of the paper and
rightwards from the left
(
i
i
)
The trilobite has been distorted by about15-20%.
c
)
(i) This suggests that the rocks that contain the fossils have
been distorted in about the same ratio. The same might well
apply to the whole region.
(
i
i
)
This could have happened when the rock was at the site of a
destructive plate margin.
(
d
)
A drawing of a suitably distorted fossil such as that in Figure 4.
Metamorphic modelling - simulating
metamorphic processes: teacher’s
notes
Level
These activities are designed for students aged 11-14 to demonstrate aspects of
metamorphism.
Topic
The aim of this unit is to simulate some of the ways in which metamorphic rocks
are formed, and to explain how both increased pressure and heat affect the formation
of the different types of metamorphic rock.
Description
Activity 1 (a class experiment or demonstration) simulates the idea of contact
metamorphism by investigating the effect of heat from a beaker of hot water
(simulating an igneous intrusion) on egg white (simulating country rock).
Activity 2 (a class experiment) simulates the formation of slate.
Activity 3 (a class experiment) simulates the distortion of fossils under pressure using
plaster of Paris models.
Context
Ideally, this unit should be taught after similar units on sedimentary and igneous
rocks.
Teaching points
As with all simulations, it is important to be aware of the ways in which the simulation
matches the real thing and the ways in which it does not. For example the
temperatures in the simulation are much lower than in real situations. Teachers
should use their discretion in deciding which of the points below to discuss with
students.
Metamorphism involves solid state recrystallisation – if melting occurs, the
resultant rock is igneous, not metamorphic.
Metamorphism involving high pressures only happens during mountain-
building episodes – pressures due to simple burial are not normally great
enough to cause metamorphism.
It is not possible to reproduce in a school laboratory the processes by which
rocks are metamorphosed on a regional scale. These activities only simulate
the physical changes which take place when rocks are put under increasing
lateral pressure, as would be found during mountain building episodes.
Timing
All three activities can be completed within a 50 minute teaching period, allowing
time for discussion and writing up.
Figure 1 Arrangement of apparatus for Activity 1
The beaker of water represents an igneous intrusion, the cooked egg white
represents the metamorphic aureole and the unchanged egg white models
unchanged country rock. The igneous intrusion is, of course, always hotter than the
country rock.
This simulation can then lead into a discussion about how contact with extreme heat
can alter the texture of existing rocks.
At this point some examples of contact metamorphic rocks, such as marble or
quartzite, are useful to show to students.
Activity 2
Apparatus
Each student (or group) will need
A box of used matchsticks, or some short lengths of spaghetti
Two rulers (approximately 30 cm)
Chemicals
The teacher will need
A piece of slate, preferably with colour bands from the original bedding (or a
photograph). Suitable samples can be obtained from a geological supplier.
The activity
Pour some used matchsticks, or short pieces of spaghetti onto the bench, so that
they lie in all directions. These represent the microscopic, flaky clay minerals in
mudstone or shale. Take two rulers and place one on either side of the matchsticks
and push them together, trapping the matchsticks and forcing them to line up parallel
to the moving rulers.
This simulates the formation of slate, where the tiny, flaky clay minerals in a
mudstone or shale are realigned at right angles to the lateral forces. Such forces
could be found near destructive plate margins, in between two approaching
continents.
In practice, the temperature also rises at the same time. This makes the clay
minerals recrystallise to form new minerals although there is no analogy to this in the
simulation.
The slate will split along the planes made by the new minerals more easily than along
the original bedding. This property is called rock cleavage, see Figure 2. You can use
the matchsticks / spaghetti to show how such rocks can split along the cleavage by
using a ruler to separate the aligned ‘minerals’. Simply slide a ruler between the
aligned pieces of spaghetti and move them apart.
Figure 2 A piece of slate, cut thinly, under the microscope showing the
cleavage running from top left to bottom right formed by the aligned
minerals. The forces causing this acted from top right and bottom left
Try to match the way the pieces are lying with a piece of roofing slate. Sometimes,
such slate shows different coloured bands lying at an angle to the cleavage, see
Figure 3. This is the remains of the bedding layers of the original mudstone or shale.
Figure 3 This sample of slate shows coloured layers at about 50
o
to
the cleavage. The coloured layers show the bedding of the original
shale.
Under conditions of ever-increasing temperatures and pressures, such slates can be
metamorphosed into higher grade metamorphic rock such as schists and ultimately
gneisses.
Figure 4 A trilobite fossil distorted by shearing forces (or alternatively by the
left-right squeezing of a fossil tilted to the left)