Download SoE 11-14 Groundwork - Earth Science Teachers` Association

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Science
of the Earth
11 - 14
TEACHERS'
ASSOCIATION
Groundwork Introducing Earth Solence.
Earth Science Teachers' Association: Science of the Earth 11-14
A series of 3-Unit Packs. The first three Packs are particularly suitable for introducing Earth Science to 11
or 12 year-olds.
Pack 1. Groundwork - Introducing Earth Science
GWl. Found in the Ground - simple classification of geological materials.
GW2. Be a Mineral Expert - introduction to minerals, using a "circus" of simple tests.
GW3. Be a Rock Detective - the use of observable properties of rocks to deduce their origins
Intended Use:
Science courses for Key Stage 3.
Aims and Requirements:
Aims and requirements are given on the Teacher Sheets for each of the three Units.
Suggested Approach:
Each Unit is intended to take one double period of 80 minutes with homework, although Unit GW2 is better if a little
more time is available. The Units follow a progressive sequence from 1 to 3, but each may be used as a free-standing
entity if required.
Resources:
Unlike many of ESTA's publications, these Units are "specimen intensive" and require the collecting together of common
geological materials before a start is made.
Suggestions are given in the text for suitable specimens, based on those used in the pilot scheme, but others are equally
useful and local initiatives should be used.
Museums may loan specimens, usually for careful use, rather than destructive tests.
Colleagues in school, or pupils themselves may have suitable materials collected during their holidays.
Local teachers groups may arrange "swop shops".
There are many dealers in geological specimens and photographs e.g.
Geo Supplies Ltd., 16 Station Road, Chapeltown, Sheffield S30 4XH.
Richard Tayler Minerals, 20 Burstead Close, Cobham, Surrey KT11 2NL.
Offa Rocks, Lower Hengoed, Oswestry, Shropshire SY10 7AB.
Landform Slides, 38 Borrow Road, Lowestoft, Suffolk, NR32 3PN.
MJP Publications, P.O. Box 23, St. Just, Cornwall, TR19 7]S.
A free mineral samples pack (with accompanying free leaflets) is available from Intermail Ltd., 10 Fleming Road,
Newbury, Berkshire RG13 2DE.
Fieldwork:
The series may be usefully followed by a field trip, either to a nearby rock exposure, or to a graveyard or town centre.
"Science of the Earth Unit I, "Will my Gravestone Last?" provides suitable guidance on such urban trips and includes
"keys" for the identification of the rocks. The ways in which rocks react to weathering are also seen on such excursions.
Acknowledgements
Thanks are due to Dominic Greenall and Alan Birchall for artwork.
Author
Peter Kennett, High Storrs School, Sheffield.
Copyright:
There is no copyright on original material published in these Units, if it is required for use within the laboratory or
classroom.
"Science of the Earth 11 - 14" Units are published by the Earth Science Teachers' Association.
ISBN 0 9501031 8 7, first published 1990; reprinted with minor amendments, 1995.
Groundwork - Introducing Earth Science
GW1: Found in the Ground
Contents:
Anfutroductitfuto eartJ;tmaterials.aj1dtheir classification.
Aims:
Toencouraged,~velop1'fte:htof pupils' own triethodsofcl<lssifying objects by
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To introduc~astar\daJ:'~tri~tl\odo£claS$ifyirtgEarth materials,
To develop.obsery~tional skills.
.
Time:
Notes on teaching the Unit
The Unit forms a useful overall introduction to Earth materials prior to more detailed coverage.
1.
Sort 'em out
Plastic storage trays are ideal for containing, sorting and even storing specimens. They may be sorted
in the tray and then need never touch the bench.
No attempt should be made to give pupils the "accepted" classification of Earth materials. Whatever
scheme they decide upon will be valid, because they chose the criteria. From this starting point pupils
may be gently steered round to seeing the need for a universal system of classification, to meet the
needs of an ordered science.
1
GW1: Found in the Ground
2.
Ask the Chief Scientist
Distinctions are usually drawn between rocks, minerals and fossils. Definitions will depend on the
age and experience of the pupils, but the following may help the teacher:
Mineral: "A naturally occurring inorganic substance with a definite chemical composition, a definite
atomic structure and physical properties which vary within known limits". This definition excludes
the more commercial use of the term "mineral" to describe almost any Earth-derived resource, such as
oil, coal, or bulk constructional material, most of which are actually rocks.
Rock: "A naturally occurring material composed of minerals or of fragments of older rocks." Many
rocks, like granite, contain a variety of minerals, whereas some, like limestone, may contain only one
mineral but many crystals of that mineral. (Note that the hardness of the material is of no
consequence - clay is a rock to the geologist!)
Fossil: "The trace of a once-living organism preserved in a rock." (This includes ''body fossils", such as
the actual shell, the replaced shell, or the imprint of the body and also "trace fossils" such as worm
burrows or borings).
3.
What's in a rock?
Most granites are coarse enough for the crystals within them to be seen with the naked eye. Some
granites contain even larger crystals than the coarse ground mass. Granite is clearly a mixture of
different minerals and therefore a rock.
Most granites contain feldspar (pink or white crystals with glinting cleavage faces); quartz (grey,
translucent and often greasy looking, with no cleavage) and mica (a soft flaky mineral. Varieties may
be black or silvery).
Granites crystallised from the molten state. The crystals are usually randomly oriented and interlock
tightly.
4.
What's in a mineral?
b) Lead (Pb) versus galena (PbS).
Compare flexibility, hardness, resistance to chipping, malleability, density. One drop of very dilute
hydrochloric acid will show the lead to be inert, but will release hydrogen sulphide from the galena.
This test is not recommended, because of the unpleasant smell and noxious fumes. It can, however, be
mentioned as giving the clue to the other element in galena (sulphur) for 4c.
Although lead minerals may not now be smelted in the laboratory, an analogy which may be carried
out is to smelt powdered copper carbonate (malachite) with powdered charcoal in a Pyrex test tube.
Heat should be applied gently at first, to prevent "blow-out".
5.
What is your home made of?
An open ended exercise. Apart from the usual metals and oil/ coal based derivatives there are also:
2
GW1: Found in the Ground
bricks from clay;
glass from pure sand;
plaster from gypsum (CaS04 .2H20);
mortar from cement (made from limestone and clay, plus fuel) and sand;
ceramics from china clay (produced by the chemical breakdown of feldspar minerals in
granite);
wallpaper "filled" with barite (BaS04) and gypsum.
paint, containing barite;
The humble lightbulb provides an excellent example of the variety of Earth-derived materials used in
everyday life. It can also lead into more geographical studies of the world occurrences of minerals
and the interdependence of the different countries as suppliers and consumers.
Use of the lightbulb diagram (Figure Tl) is recommended as a basis for class discussion; either on the
overhead projector or as a handout.
Students could be asked to plot the sources of the various components on an outline map of the
world. The original diagram is by Dr. M. Tuke, "Geology Teaching", VoI2.4. December 1977.
extracted from the air
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mining
GW1: Found in the Ground
Your group has a jumbled collection of specimens. Each specimen has come out of the ground,
most of them from different parts of Great Britain.
Scientists learn to recognise these items and they try to use the clues they contain to work out how
they were formed. Some of the things are of value to people and are used as raw materials in our
industries.
Try the following, working quietly in your group:
1.
Sort 'em out!
Look for similarities in
different specimens, Le.
try to decide if any of
them have anything in
common with other specimens, even if you have no
idea what they are. Try to
divide the collection into
- - --~--three or four groups, each
group based on some
property which they all have. For example, you might decide
to place together specimens which show evidence of some
once-living animal etc. Lay your three or four groups out
neatly.
Don't worry if other pupils are using different properties to
classify their specimens - it is your ideas which are important.
2.
Ask the Chief Scientist
2.1
When you have finished classifying your specimens,
discuss your findings with your teacher. You will then be
told one method of grouping (Le. classifying specimens)
which geologists use.
2.2
Write down the usual geologist's classification in your
book.
2.3
Re-classify your collection on the bench, using the geologist's scheme which you have been given.
Note that your method was not "wrong". You thought
very carefully about what you were doing, and your
method worked for you. It's just that we need to use a
system which everybody agrees upon, or it would get a
bit chaotic! Different scientists would not be able to
understand what other scientists were talking about.
4
GW1: Found in the Ground
3.
What's in a rock?
a)
Examine the rock with the white spot. It is a type of
granite.
b)
How do you know that it is a rock and not a mineral?
c)
Describe it in writing, as fully as you can, trying to say
how many different minerals there are in it, and what
they look like. You are not expected to name the minerals!
You might find it useful to draw a diagram of a small part of
one face of the rock (e.g. 4cm2). Don't forget to label it and to
give it a scale.
If the rock has one polished surface, you could try using tracing
paper for your diagram of its minerals.
4.
What's in a mineral?
You have now discovered that there is a difference between a
rock and a mineral.
Minerals are, in a way, the "building blocks" from which rocks
are made. Some, but by no means all of them, are also of economic value.
But is a mineral composed of one element only, or can it be
made up of more than one?
To find out:
a) Pick out from your collection the mineral which most
resembles a piece of lead. This mineral is called galena.
Galena is not a rock-building mineral, but occurs in veins
running through other rocks, as in the Pennines and
Mendips. You will also be given a small piece of lead
sheet.
b) Look carefully at the galena and at the piece of lead. Does
the galena have the same properties as the lead metal? Test
both specimens in any way you think useful. Record these
results in two short columns in your book.
c) Try to find out the other substance which combined with
the lead millions of years ago to produce the lead mineral
called galena.
You have discovered that galena is a compound, i.e. it is made
of more than one element combined together. Most minerals
are compounds, although some are just one element alone, e.g.
diamond (the element carbon) and gold. Pure lead does not
occur on its own in the natural world.
5
GW1: Found in the Ground
5.
What is your home
made of?
Take a good look around
your bedroom or kitchen
at home. Draw three
columns:
a) In the first column, write down the names of several objects
in the room (e.g. saucepan) and several different materials
from which your home is built.
b) In the second column, note down the materials of which the
objects are made, (e.g. saucepans from aluminium)
c) In the third column, find out and write down the names of
the raw materials that are the sources of the materials you
can see. If you need help use books or ask someone. (e.g.
the mineral bauxite is the source of aluminium)
Apart from furnishings made from wood or soft furnishings of
cotton or wool, you have probably found that most of your
home is made from things which were found in the ground.
Clearly, it is very important for us to classify them, so that we
all know what we are talking about.
6
Groundwork - Introducing Earth Science
GW2: Be a mineral expert
Contents:
An introduction to minerals.
Aims;
To enable pupils to identify different methods of sorting out minerals and
to tryout their ideas on named minerals.
To enable pupils to.use their experience of mineral testing to identify
"unknown" minerals.
To encourage pupils to identify the links between mineral properties and
their uses,
Time:
2 to4periods of 40 minutes,depending.oo the number of specimens
available and thethoroughriess oftl\e tests.
Organisation:
Pupils wo~~ingr0tlPs. E~ch~u~ f$giv~r\astmt11 set of"Unknown#
minerals•. ··1'11eysuggestsult~leteststodiStingU~·betweenthe minerals
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Notes on teaching the Unit
The Unit is best used after a general introduction to Earth materials, such as the Unit, "Found in the
ground".
7
GW2: Be a mineral expert
1.
What's in a name?
An attempt to explain the several meanings of the term "mineral".
If the pupils have not already done so, the distinction between a mineral and a rock might usefully be
established, e.g. by class discussion around a large specimen of coarse granite. (See "Found in the
ground")
2.
Putting minerals to the test
Issue a set of "unknown" minerals to each group of about 4 pupils. Specimens used in the "pilot"
scheme were vein minerals from the Peak District mining field, namely: calcite, barite, fluorite,
sphalerite and galena.
Do NOT issue the table of mineral properties (Data Sheet 1) yet.
2.1
This is intended as a fairly quick introductory session, with little comment, designed to start pupils
thinking and observing, without any preconceived ideas.
Pupils usually suggest:
colour: lustre ("shininess"): crystal "habit" (general shape): transparency ("see-through"): translucency ("see-into"): opacity: density (help them to distinguish from "weight"): hardness: cleavage
(breakage along regular planes): fracture (breakage in an irregular way).
2.2
Sets and accompanying cards should be prepared in advance and placed at intervals around the lab.,
in plastic trays.
Pupils visit each "station" in turn, carry out the test and record their findings.
Notes on some of the tests:
Density: Pupils are expected to place the specimens in order of increasing relative density by the
simple process of "hefting" them, i.e. "weighing" them in their hands.
Streak: This test is only of use for opaque, relatively soft minerals. Other minerals usually produce
white streaks, or simply scratch the tile.
Cleavage: The cleavage test should be demonstrated under the teacher's supervision, in the interests of
safety and conservation of specimens! Any common mineral that cleaves well may be used, e.g.,
calcite, gypsum or halite (rock salt).
An 18th Century mineralogist dropped a superb "dog-tooth spar" specimen of calcite in a friend's
collection. It smashed into rhombohedral fragments, which apparently bore no relation to the original
crystal. However, he showed that the rhombohedra could be used to "rebuild" the crystal and thus
nearly laid the foundations of molecular theory! (Figure T1 overleaf)
8
GW2: Be a mineral expert
Figure T1. An 18th Century diagram to show how a crystal of dog-tooth spar (calcite) may be thought of
as being built up from rhombohedral units.
Pupils do not need to smash any specimens. Incipient cleavage planes are frequently visible within the
mineral.
Acid test: Hydrochloric acid may be prepared by diluting bench acid with water in the ratio 1 to 3. Any
carbonate will produce carbon dioxide upon addition of this acid, usually with effervescence. Avoid testing
galena with acid: it gives off foul-smelling hydrogen sulphide.
Specimens for the "circus" of tests.
These may well depend upon what is available within school. One specimen of each named mineral is
needed for each of the sets. The "pilot" scheme used the following:
Density: Labelled specimens of gypsum, quartz, barite, galena.
Habit: Well-formed labelled specimens of quartz, garnet, fluorite.
Lustre: Labelled specimens of quartz, limonite, gypsum (var. "satin spar"), galena.
Colour: Several different unlabelled coloured varieties of quartz, e.g. amethyst, rose quartz, yellow Cairngorm, smoky quartz, etc.
The same could be done with feldspar or with fluorite.
Streak: Labelled specimens of galena, sphalerite, haematite, pyrite ("Fool's Gold")
Acid test: Labelled specimens of fluorite, quartz, gypsum, barite, calcite. Any minerals will do, so long as
there is one carbonate. The commonest is calcite.
Cleavage: calcite and halite (rock salt) are both readily available and cleave easily.
Hardness: Unlabelled specimens of gypsum, calcite, fluorite and quartz.
Labelling may be done temporarily with sticking plaster and ball-point pen. A better job is done with a
Tippex blob, labelling with a draftsman's pen and over-varnishing.
9
GW2: Be a mineral expert
3.
Expert at Work!
3.1
Pupils should return to their places and to the set of "unknown" minerals.
They should be issued with the Data Sheet of mineral properties and allowed to observe and test the
minerals in front of them. They will need to check their answers with the teacher.
3.2
Answers:
calcite v. fluorite
fluorite v. barite
galena v. sphalerite
4.
What's the use?
4.1
Answers:
Calcite (limestone)
Fluorite
Barite
Galena
Sphalerite
- acid test (hardness or crystal habit would do)
- density (crystal habit would do)
- streak or density
- blast furnace etc.
- source of fluorides in toothpaste, etc.
- dense drilling "mud" etc.
- lead, e.g. car batteries
- zinc, e.g. galvanising etc.
Many other uses are equally valid.
4.2
Answer:
In modem separation plant, the mixture of minerals is crushed. Low density waste is separated from
higher density minerals by heavy media methods. Further crushing takes place. Final separation is
done by froth flotation, in liquids of various compositions.
Earlier, less efficient methods mostly used running water to carry away low density minerals and
leave behind the wanted higher density ones. A good model can be made using a piece of plastic
guttering with double-sided Sellotape baffles at intervals across the length. A slurry of mixed minerals in water is poured repeatedly down the gutter until separation is achieved.
10
GW2: Be a mineral expert
Cards for use with "Circus" of minerals tests
(Note: where minerals are named, these are ones used in the "pilot" scheme. Others may equally
well be used, depending on availability in the school.) These sheets should be printed on card,
folded, so as to bring the answers on to the back of each card, and cut. They are best covered with
clear plastic.
I
I
I
Pick up each specimen in turn and see if you
I
can put them in order of increasing density as I
you put them down. (Density is the weight of I
something in relation to its volume: e.g. a
I
piece of lead weighs more than a piece of
I
wood of the same size)
I
I
The minerals are:
I
Barite
I
Galena
I
Gypsum
I
Quartz
I
I
Check your answers from the back of the card I
- afterwards!
I
Density
Density answers
The order of density is:
Gypsum (2 x density of water)
Quartz (2 1 / 2 X density of water)
Barite (41 / 2 x density of water)
Galena (71 / 2 X density of water)
Thus, gypsum is the least dense of the minerals in this set and galena is the most dense.
I
Lustre
Lustre answers
This word describes the way in which the
minerals reflect the light. Try to match the
descriptions given below to the list of miner.;.
als by looking at the set laid out here. The list
on this side of the card is in jumbled order
Lustre
metallic
glassy (vitreous)
dull
silky
metallic
glassy
dull
silky
- galena
- quartz
-limonite
-gypsum
(You probably were not given a diamond in
the set! Diamond is especially valuable because of its very bright" Adamantine" lustre,
which makes it sparkle in the light.)
Mineral
quartz
limonite
gypsum
galena
Answers on the back - don't cheat!
11
GW2: Be a mineral expert
I
Colour
Colour answers
The colour of a mineral is a help, but we have
to use it carefully, because some minerals may
have more than one colour. These specimens
are all of the same mineral.
Write down the different colours which this
one type of mineral has.
Write down which other properties of the
specimens might tell you that they are of the
same mineral. Some suggestions appear on
the back of the card.
If the specimens are all of the same mineral,
then they will probably have the same:
hardness
lustre ("shininess")
crystal habit (shape)
density
T
I
Streak
I Streak answers
I
The labelled specimens in this set are all
Galena
- thick grey
I
opaque, i.e. you can't see into them or through
- buff or off-white
Sphalerite
I
them. It is difficult to tell their true colour.
Haematite
- browny-red
The streak test is a way of getting a powdered I
Pyrite
- thin green-grey
I
sample, which may show the colour better.
I Is this what you found?
Try to make a short mark with the mineral on
I
the unglazed side of the tile.
Note the colour of the streak you produced on I
I
the tile and whether it is a thick or a thin line.
I
See over for the textbook answers - after you
I
have done the tests!
I
Acid Test
I
Acid test answers
" (You are using very weak acid, but do quickly
wash it off with water if you spill acid on
yourself or your clothing)
There is only one carbonate mineral in this
set. It is Calcite:- CaC03
Minerals which contain any carbonate will
fizz when dilute hydrochloric acid is added.
Put one drop only of acid onto each of the
specimens in turn and try to find out which
contains a carbonate.
When you have finished, dry off the acid with
a paper towel.
See back for answers - afterwards!
12
GW2: Be a mineral expert
Hardness
Every mineral has a fixed hardness (i.e. it is always the same for every specimen of that mineral).
A mineralogist named Mohs tested hundreds of minerals and drew up a scale of hardness from 1
to 10. Each mineral in the scale will scratch all the minerals below it in the list, but cannot be
scratched by them.
Mohs' Scale of Mineral Hardness
10
Diamond
9
Corundum
8
Topaz
7
Quartz
6
Feldspar
5
Apatite
4
Fluorite
3
Calcite
2
Gypsum
1
Talc
Steel needle scratches minerals of hardness 5 and below.
Now test the minerals in the set to find out their hardness on Mohs' Scale.
Use the steel object, a "copper" coin and your fingernails (unless you have bitten them down!)
Press fairly hard against the mineral and try to scratch a short line on the specimen. Blow away the
dust, to be sure that you have really marked the mineral. Double check by testing the other way
round, i.e. check that you cannot scratch the object with the mineral.
Work out the mineral's hardness as closely as you can from the table.
Mohs' Scale can be used to describe the hardness of any mineral, but to make it easier, the ones in
front of you all appear in the Scale. Work out which is which.
Hardness answers
Gypsum
Calcite
Fluorite
Quartz
-2
-3
- 4 (but you might have failed to scratch it - you have to press hard)
-7 (but all you can say is that it is harder than steel, i.e. more than 5)
13
GW2: Be a mineral expert
I
Cleavage
Cleavage answers
Some minerals break in a very regular way.
This is called cleavage.
If you were using calcite, the cleavage fragments are called rhombohedra. They look
rather like squashed cubes.
Others fracture, like glass, with no real pattern to the breakage.
A really good crystal of calcite, before smashing, may look like a dog's tooth and this form
of the mineral is known as dog-tooth spar".
Put safety goggles on.
11
Watch your teacher break the piece of calcite
with the hammer.
What is the shape of the fragments? Draw an
example.
Look at some really tiny pieces through a
hand lens. How does their shape compare
with the bigger pieces?
The regular surfaces you can see are called
cleavage planes.
(In practice, we don't have to damage a specimen - lines can usually be seen in it, without
the need to hit it!)
Note to Teachers:Crystal habit answers
Crystal Habit
This term really means the shape and proportions of the crystal.
Try drawing one or more of the crystals.
Note: All these crystals have been formed
naturally and have not been cut in any way.
Please don't scratch them. They include:
(Nil. Any 2 or 3 well-formed crystals will suffice
for this test. Avoid any which have been artificially
cut. Show the names in the space on the card.)
I
14
GW2: Be a mineral expert
1.
What's in a name?
The name "mineral" is used in many different ways:
We need "minerals" in our food for healthy living.
We consume lots of "minerals" in less healthy living when we
drink fizzy pop!
When Governments talk of the "mineral" wealth of their countries, they usually include resources such as coal and oil.
To geologists, "minerals" are naturally occurring compounds
of inorganic origin, so coal and oil are not included.
Minerals, in this sense, have definite chemical compositions
and they have properties which can be tested.
In this Unit, we are going to use some of these properties to
identify some "geological" minerals. But first, you can decide
for yourself the kind of things which might be useful.
2.
Putting minerals to
the test
2.1
Look at the minerals.
In the tray you have a collection of minerals.
An example of one of the
differences is that the
"shininess" varies - some
glisten and others are dull.
(The proper word for
"shininess" is lustre.)
~.. ~/
Check your list with your teacher.
You will have found several differences between the specimens
just by looking at them or picking them up.
They can also be tested in different ways.
2.2
To learn how to do these
tests, there are some
other sets of minerals
placed around the room.
When you are told, visit each of these sets in turn. At each set:
i) read the card,
ii) carry out the test,
iii) record the results carefully in your book, using the
headings given on the cards.
You will probably need to spend about 10 minutes at
each mineral set before you move on to the next.
15
GW2: Be a mineral expert
3.
Expert at Work
3.1
Now that you are an expert mineralogist, use some of the
tests and observations you have learned to identify the
"unknown" minerals in the set you were given at the
start.
N.B. 00 NOT HIT THE SPECIMENS TO SEE HOW
THEY CLEAVE. You will see plenty of evidence within
the minerals of how they would break if hit!
Write down your results as you work.
Use the table on Data Sheet 1 to help you to identify the
"unknown" minerals.
3.2
Use the table of mineral properties to write down one test
which would enable you to tell apart the minerals in the
following pairs:
i) calcite and fluorite
ii) fluorite and barite
iii) galena and sphalerite
16
GW2: Be a mineral expert
4.
What's the use?
4.1 Try to find out the uses of these minerals. You can either
look them up in books, or you could try connecting the
"tops and tails" in the following jumbled list:
Mineral
Uses (not in right order)
Calcite (in the form
of limestone)
ore of lead (used in car batteries).
Fluorite
making a heavy drilling "mud" for use in oil boreholes.
Barite
ore of zinc (used in galvanising steel).
Galena
adding to blast furnaces to help in smelting iron. Making lime.
Sphalerite
making chemicals to add to toothpaste to help cut down tooth
decay.
Very many minerals have important industrial uses. However,
they often occur all mixed up together and the firms quarry or
mine a mixture of the minerals. Then they have to separate
each mineral from the others, many tonnes at a time.
4.2
Imagine that a firm needs to separate galena from
fluorite.
Use your knowledge of the properties of the minerals to
suggest a method which the firm could use to do this.
Try to draw a diagram to show how your method would
work.
(Hint: The old-time miners invented two processes to
separate minerals, called jigging and buddling. Both
involved the use of water).
17
GW2: Be a mineral expert
Table of Properties of some Common Minerals
Mineral
Property
Calcite
Fluorite
Barite
Galena
Sphalerite
Colour
white, pink,
colourless
blue, yellow,
green,
colourless
white, pink
dark grey
black to
brown
Streak
white
white
white
thick grey
pale brown
or off-white
Lustre
glassy
glassy
glassy to dull
metallic
metallic to
glassy
Hardness
3
4
31 /
21/2
31 /
Density
moderate
moderate
surprisingly
dense for a
white mineral
very dense
moderate
Acid test
fizzes
violently
nil
nil
DO NOT TEST
nil
Habit (shape)
"dog-tooth" ,
shape, or
more often
rhomb-shaped
cleaved
fragments
cubic,
sometimes
with
corners
missing
often "cockscomb"
structure
otherwise
layered
often broken
into cubic
cleavage
fragments
good shapes
rare
18
2
2
Groundwork - Introducing Earth Science
GW3: Be a rock detective
Contents:
A simple introduction to rocks of sedimentary, igneous and metamorphic origin.
Aims:
To enable pupils to observe carefully and to draw reasoned conclusions from their
observations.
To encourage pupils to devise a "key'! for the identification of rocks, based on their
own experience in handling them.
Time:
Two periods of 40 mi.J:1utes plus extension or homework.
Organisation:
fupihi work in gr?Ups.~~chgtot1piSgiven atrajrqf 4rI?Cks ofvat<iedorigins.
They examinether~caref,"lly~dselectcorrf;lFtr~sponsesoJ;\a work,sne.etto .
help describethem.Theto~a~~~bY~"tl1Atcliit"exetdSe•.. ' . ..'
fupilsthenexatn4le a Slng~e~tofspedmens which con~inrathermore eviden{;e
of theirorigm, andtrytodeducethe~toryof~ach ro~k.. .... . . .. . . .
Working in. groups odndividually,pupilS devise a simple "key".f()t ideutifidition
ohocks,and suggest whic1l oftl1el'OFks is~oSt~uitableforcertainus~s. ....
ay
.
be done c()ncurrentlYwiththe above exercise, to ease congesti0naroUlld the .'
setohpedmens. .
Requirements:
Eachpupil.willneed; .•• retUri:iable.copies.of·Piipg..$h~e~.lto4
an expendable copy"f Data Sheet 1;
... .
Each group will heed:
Handlen~s . . . . . . .......... ........ i . ... .... .. .... ...... ". . . ............ ...... . . '.' ................ ..... . .... ... ..... ........... .......... .<
.Atray of 4rocksi labelled~/S, T,u.'llter~ -whiehfit theanswersinData$b~~
1 ail;!!
.............. ' . . .•. . . . •. ............. . . . . . . •.•.•. .•. . .••.. ...... ......................... '.' ...........................................................
E,;; a.lava'Yith ga,$holes, eitherop~nl),oles;,orot\esw~have~nfill.ed irilattlr
by mi.J:1er~l$: . .•.
\... ...... . •.•.'. ' . ' i . •.• • . ...•••.. . •.•...... .
..
..
S ;;agranit~J e.g;f!6~a<l~olis~edshopfront
T;;a coal'$esa~stone,sufl'las apiece of "millstone. grit".
U ;;a schistiwi~plenty o(g~tingll.licaonitstt"t~~r!~ce~...... ". ...... . . . . . . .'. . ....
The dass\ViU need; .. a se~ of" go()dF1$p~imetlS, eachsnowingplentyofevi4~ce
()fits formaijon.(Seenoteson ~tiort3) . . . . .
.
Att exan:lplE!of anyi4entific~tion~/Key" £01:4;2.
Notes on teaching the Unit
This Unit is best used after a general introduction to Earth materials, such as in the Science of the Earth
Units, "Found in the Ground", and "Be a Mineral Expert".
1.
Find the clues
Set out one tray of specimens per group of pupils, hand lenses and a copy of Data Sheet 1 per pupil.
Pupils work at their own pace and record answers on the sheet. The object is to encourage careful
observation and not to expect pupils to give names to rocks at this stage.
The Data Sheet will need revision if markedly different specimens are used. Aim for a variety of
rocks, to represent sedimentary, igneous and metamorphic origins. The specimens which have been
successfully used with Data Sheet 1, as it stands, are:
19
GW3: Be a rock detective
R =an ancient basalt lava. Sometime after the lava was erupted, minerals being carried in ground-water may
have penetrated the rock and may have become deposited in the gas holes. Some of these may subsequently
weather out, leaving empty holes.
S =a granite, consisting of three main minerals: quartz (grey, glassy), feldspars (white or pink) and micas
(glinting surfaces, black or colourless). The rock crystallised deep in the Earth's crust.
Both R and S are of igneous origin, but in the lava, the size of the grains in the ground mass (i.e. the body of
the rock) is too small to be seen with the naked eye. This is because of the very fast cooling rate of the
magma (molten rock).
The granite also formed from a magma, which crystallised much more slowly several kilometres deep in the
Earth's crust. This resulted in larger crystals being produced, which are easily seen with the naked eye.
Deep-seated igneous rocks, such as granites, are revealed at the Earth's surface only after erosion has
stripped off the overlying rocks.
T = coarse sandstone. A typical piece of such"grit" often consists of sub-angular grains of quartz (glassylooking) and partly decomposed feldspar (creamy colour), set in a cement of iron oxides (brown).
Sandstones are sedimentary rocks. Some of them contain fossils, unlike the vast majority of igneous and
metamorphic rocks.
The coarse sandstones of the Millstone Grit Series are widely represented in collections. They would have
been deposited in a huge river delta which must have covered most of northern Britain in Carboniferous
times.
U =a schist, which is a metamorphic rock produced from clay-grade rocks under intense directed stress and
raised temperature deep in the Earth's crust. This caused recrystallisation in the solid state, the new minerals
being formed from the existing elements in the rock, without anything other than water being removed or
added.
The most obvious feature of the schist is the sub-parallel orientation of the many mica crystals: Schists are
usually fissile, i.e. they will split roughly along the planes of mica crystals, but they do not produce planar
cleavage planes as in slate. Slate is a better-known metamorphic rock, which has not been so intensely
heated or squeezed. It might provide a ready alternative to schist if the latter cannot be obtained, but it is not
so spectacular! A third alternative is a gneiss, which has been even more altered than a schist.
2.
"I name this rock ... "
The purpose of this section is to introduce pupils to the names of some common rocks, including the
ones which they have been handling. It is a simple matching exercise, the answers to which will
depend on the specimens available for Section 1.
3.
More clues
This calls for your very best rock specimens! (Photographs may be used instead). Rocks that have
been used successfully included:
v - a shale, formed by mud settling from suspension under very low energy conditions. Pupils can
imitate this with muddy water in a beaker, which is left to stand.
20
GW3: Be a rock detective
If the shale contains a fossil, much more can be said. For example, the presence of an ammonite
would imply a marine origin, whilst a well-preserved tree leaf imprint might suggest a low energy
swamp environment.
W - A ripple-marked sandstone. The ripple marks were formed by to-and-fro wave action, as on any
modem beach. Pupils are usually able to bring their own seaside experience to bear in solving how
the rock was formed.
x - A conglomerate (pebble bed).
This was deposited by fast-flowing water currents on a beach or a
river bed. Again, pupils' own experience is helpful here.
Y - A gneiss with large garnet crystals protruding from it. This is a metamorphic rock, formed under
conditions which were hotter and under more pressure than those in which a schist is formed. Garnet
crystals normally only grow in the rock when the pressure has been high. Pupils should realise that
no-one has seen such rocks forming, so here is a case where their own experience is less applicable.
Z - A very fossiliferous limestone, indicating a former shell bank or reef environment. The types of
fossils can often be used to show whether it was a marine or freshwater environment, and may also
enable the age of the deposit to be found.
4.
Call the next case
These exercises have been designed to reinforce the ideas the pupils have gained in class and then to
encourage them to apply their knowledge to new situations.
4.2
Show pupils the principles of making a "key", if this is new to them. Any non-geological key may be
used as an example. Their own keys will vary from pupil to pupil. A simple key for rock identification is published in the "Science of the Earth" Units, No: I, "Will my Gravestone Last?" and No: 7,
"Neighbourhood Stone Watch".
4.3
The most likely answers are:
a) slate: b) clay: c) limestone: d) clay: e) marble: f) and g) any except clay and schist. The popular
"Westmorland Green Slate" is actually a volcanic ash which has been metamorphosed.
21
GW3: Be a rock detective
1.
Find the clues
Geologists have sometimes been
nicknamed "rock-bashers".
In areas of beautiful scenery we are
careful not to spoil the countryside
by hammering at rock faces, but in
working quarries specimens may
be collected without causing too
much damage.
You can also find interesting rock
specimens lying loose on the beach
or in stream beds. Every rock
contains enough evidence to tell
the geologist how it was formed:
some are so interesting that it is a
bit like solving a detective story!
See what you can find out from the rocks in front of you.
1.1 Look carefully at rocks R, 5, T and V, preferably using a
hand lens to see the detail. Data Sheet 1 will help you to
kllow what to look for, although you will probably think of
other things too.
Use Data Sheet 1 as a recording sheet for your observations.
As you study each rock, cross out the wrong answers on the
sheet, so that only correct observations remain.
Study all four rocks before moving on to the next question.
1.2 Now, look through each of your descriptions of the rock
specimens.
Try to decide which description fits each of the following
ways in which the rock might have been formed:
a)
Which specimen was formed from loose sand grains which
may have been washed down by a river and then naturally
cemented together?
b)
When molten lava erupts from a volcano it often contains a
lot of gas, which bubbles out, rather like the steam when
you are cooking thick porridge.
Which specimen was formed from a lava flow?
22
GW3: Be a rock detective
c)
When molten material crystallises to form solid rock, the
crystals usually fill up all the space by interlocking together. Melts which crystallise deep down in the earth cool
slowly, producing fairly large crystals. Which
specimen was formed by crystallising from the molten
state deep down in the Earth's crust?
d)
When rocks are squeezed under great pressure, but not
melted, minerals are produced which are lined up parallel
wi th each other.
Which specimen was formed from another rock which was
heated and squeezed under great pressure deep in the
Earth's crust?
2.
"I name this rock .... "
So far you have been asked to study and describe the rock
specimens, without naming them. Like most scientists, however, geologists need to find names for the objects they study,
so that they can communicate about them with each other.
Whilst you were dealing with Section I, you may have realised
that there are three main ways in which rocks are produced.
Two of the rocks you studied formed when a molten rock
cooled down, forming crystals. Eventually they became solid
rock. These are called igneous rocks, which either crystallised
from a lava flow at the Earth's surface, or crystallised deep
down in the Earth.
One other specimen was formed when an area of land was
worn away by wind, rain and rivers to produce sand. The
sand was carried to the low part of the river or to the sea,
where it settled out and later became cemented to form a
sandstone. Rocks made in this way are called sedimentary
rocks.
The last specimen was produced by heating and squeezing
rocks deep within the Earth's crust. The rocks did not melt,
but crystals grew in the solid rock so that it became altered to
the metamorphic rock which you have seen.
Table 1 names some examples of rocks from each of these three
different groups;
Sedimentary rocks
Igneous rocks
Metamorphic rocks
limestone
clay
sandstone
basalt lava
volcanic ash"
granite
slate
marble
schist
11
Table 1. Rocks of different types
23
GW3: Be a rock detective
2.1 Read the brief descriptions of each of these rocks given
below. Then try to match up the specimens R, S, T and U
with the correct description. This will enable you to "name
this rock. .. "
limestone - rock containing carbonate minerals (which fizz with
dilute acid), often composed of the hard parts of dead
organisms.
clay - soft rock which can be moulded like Plasticine, with
particles which are too small to see.
sandstone - rock composed of visible sand grains cemented
together.
basalt lava - a dark volcanic rock often containing gas bubbles.
volcanic "ash" - rock composed of tiny fragments of rock,
blasted out of a volcano. Usually layered and often green
coloured.
granite - rock consisting of large interlocking crystals with no
spaces between them.
slate - a rock in which the very fine parallel mineral structure
causes it to break or "cleave" easily into thin flat sheets.
marble - a rock containing interlocking carbonate minerals
(which fizz with dilute acid), often colour-banded and usually
without any fossils.
schist - rock with slightly wavy layers which glistens because of
many small mica crystals parallel to the layers.
3.
More clues
The next specimens all have something extra about them, which
will enable you to work out even more about the ways in which
they were formed.
3.1 Study the set of specimens V, W, X, Y and Z. They all
contain clues about their origin.
a)
Draw a scaled diagram of each specimen or photograph.
b)
Describe it briefly.
c)
Use the clues you have seen to try to write down how the
specimen was formed in the geological past. (Hints: Use
the ideas you have already learned in Section 1. Use your
own experience of things you have seen around you, e.g.
on holiday at the seaside.)
24
GW3: Be a rock detective
4.
Call the next case
4.1 Use your rock detective work so
far to write down a list of the
sort of things you need to look
for in a new rock. Try to keep
the list in a sensible order.
When you get home tryout
your list on other members of
your family, using a rock from
the garden, or a "mantelpiece
specimen" .
If you have ever tried to identify a
strange plant or a butterfly, you have
probably used a "key" to do so.
4.2 Using what you have learned about naming rocks, draw your
own key for identifying the nine rocks in Table 1.
4.3 Using the list in Table I, choose one rock which would be best
for each of the following purposes:
a)
roofing your house
b)
making pottery
c)
making lime to neutralise acid soils in the garden
d)
making house bricks
e)
carving a statue
f)
making an ornamental frontage for a large bank building
g)
building a fireplace in your best room at home.
25
GW3: Be a rock detective
Find the clues - observation recording sheet
As you study each rock R, S, T and V, cross out the wrong answers on
this sheet, so that only correct observations remain.
Do it carefully and really look hard at the specimens before you use
your pencil!
Add extra information you have gained by using all your senses, apart
from taste.
RockR
The colour of this rock is mostly: pink; brown; dark grey, other ..... ?
The rock has circular features in it which are: bullet holes: empty gas holes: gas holes, later filled
in with minerals: worm burrows: moulds of fossils.
The minerals which make up the rest of the rock are: very easy to see; fairly easy to see; very
difficult to see.
The rock contains: many fossils; a few fossils; no fossils.
Other observations......................................................................................................................................... .
RockS
The colour of this rock is: yellow; mottled grey and white, or grey and pink; dark grey, other .... ?
How many different kinds of minerals can you find in this rock? 1; 2; 3; 4.
The rock is made of crystals which are, on average, about:
3mmacross.
1/
2mm; 1mm; 2mm; 3mm; more than
The crystals look as though: they fit together in an interlocking way; they were once loose round
grains which have been cemented together.
The rock contains: many fossils; a few fossils; no fossils.
The rock: has gas bubbles in it; has gaps between the crystals; has no gaps between the crystals.
Other observations........................................................................................................................................... .
26
GW3: Be a rock detective
RockT
The colour of this rock is; dark grey; light brown; green.
The rock consists of separate grains which, on average, are about: 1/4mm; 1/ 2mm; 2mm; more
than 2mm across each grain.
The grains look like small pieces of: coal; glass; chalk; shell.
The shape of each grain is: very angular; partly rounded; well rounded.
There are: many fossils; a few fossils; no fossils.
The surface of the rock: absorbs water; does not absorb water.
Other observations ....................................................................................................................................... .
RockU
The colour of this rock is: dark brown; silvery grey; green.
How may different types of minerals can you see in the rock? 1; 2; 3; 4.
The minerals are: very easy to see; fairly easy to see; very difficult to see.
The minerals are: all jumbled up; arranged in thin sheets; arranged in rough layers; arranged in
thick bands.
The rock contains: many fossils; few fossils; no fossils.
Other observations ............................................................................................................................................ .
27
Earth Science Teachers' Association: Science of the Earth 11-14
Coverage of the National Curriculum for Science (1995 version)
Most of the material in these Units is designed to introduce Earth materials to pupils in the early stages of Key
Stage 3. Under the heading, "Materials and their Properties", the National Curriculum requires that, "Pupils
should be taught that rocks are classified as sedimentary, metamorphic or igneous on the basis of their processes offormation, and that these processes affect their texture and the minerals they contain
Some aspects of "Systematic Enquiry" and "The Application of Science" may be delivered through these
Units. There is also scope for developing pupils' experience of "Experimental and Investigative Science", in a
context which is a little less familiar than their earlier work in a laboratory.
If.
A simplified analysis of skills is given below.
Analysis of skills
Designing and planning an investigation
Practical investigation
GWl GW2 GW3
Decision making exercise
./
./
./
Experimental investigation
Data collecting and recording
Data plotting exercise
Analysis of skills
GWl GW2 GW3
Solving problems by applying results
Compiling a report
./
./
./
Calculation
Three-dimensional thinking
Data manipulation exercise
Other ESTA Packs in the "Science of the Earth 11-14" series are:-
1. For the revised (1995) National Science Curriculum at KS3:
GW
ME
M
SR
HC
FW
E
Groundwork: introducing Earth science
Moulding Earth's surface: weathering, erosion & transportation
Magma - Introducing igneous processes
Secondhand rocks - introducing sedimentary processes
Hidden changes in the Earth: introduction to metamorphism
Steps towards the rock face: introducing fieldwork
Power source: oil and energy
2. For enhancement of teaching beyond the strict confines of the National Curriculum at KS3
or KS4:
LP Life from the past: introducing fossils
PP Power from the past: coal
WG Water overground and underground
ESTA publications are distributed by: Geo Supplies Ltd., 16 Station Road, Chapeltown, Sheffield S30 4XH.
"Groundwork" is designed and typeset by Geo Supplies Ltd. Printed in England.