BUILDING CONCEPTUAL UNDERSTANDING IN … of research into students ‘ ability to understand, classify and identify rocks; (ii) to suggest reasons why approaches to teaching about

ABSTRACT

Studies of students’ understanding about rocks indicatemost young students do not have a scientificunderstanding about rocks. This persists into adulthood.Students’ first encounters with rocks are frequentlyconducted through descriptive observational studies.This approach is inductive and can create difficulties inleading students to compartmentalise rocks and see eachrock as a singular entity. This fails to help studentsrecognize and derive generalizations about the fund-amental characteristics common to different generic rock groups. Researchers have suggested that input abouttechniques and conceptual frameworks which geologists use may prove more successful in developing students’understanding, providing they are intellectually safe and accessible. A new pedagogic approach which matchesthese requirements has been used to create a sequence ofinvestigative activities enabling students to speculate,hypothesise, observe, test, reason and infer about thecharacteristics of rocks. The approach is framed by twoquestions (i) What are the key characteristics of differentrock groups?, (ii) How did the rocks acquire thesedifferent characteristics? Using the knowledge and un-derstanding acquired, students have demonstrated theycan assign rocks into appropriate generic groups usingthe same criteria as Earth scientists. They can relate thetextural characteristics to a range of rock properties.

Keywords : Education - precollege; earth science -teaching and curriculum; petrology - general

INTRODUCTION

In the UK the study of rocks has become an increasinglyestablished part of the science curriculum. In the 1970sand 1980s there were several influential sciencecurriculum development projects that included thestudy of rocks and some of these selected rocks as a major topic (Harwood, 1987). In 1989 a National Curriculumfor Science was introduced and throughout severalrevisions the study of rocks has remained a componentin the program of study for students aged 5 to 16 years.(Department for Education and Employment andQualifications and Curriculum Authority, 1999). One ofthe main reasons for studying rocks within the context ofa science curriculum should be to help students to gain ascientific perspective and understanding about rocks,with the aim of enabling students to use the methods ofthe Earth scientist to investigate and classify rock,develop interpretations about the modes of formation ofrocks and assess the properties of rocks. Howeverinvestigations into children’s understanding and per-ceptions of rocks indicate that their concept of whatconstitutes a rock, their perception of the importantattributes and how rocks are classified, do not appear tomatch those held by Earth scientist.

The particular characteristics of a rock to which anEarth scientist assigns significance are not necessarilythose characteristics that are most obvious to students. Earth scientists classify rocks by their processes offormation into igneous, metamorphic and sedimentaryrocks (generic rock groups). The mode of formationaffects the texture and composition of a rock. It is theobservation and description of the textural andmineralogical characteristics of a rock that enables anEarth scientist to classify a rock and make inferencesabout its mode of formation. To gain a proper scientificunderstanding about rocks, it is important to be able tofirstly recognize the determinant characteristics of a rock, and secondly to understand their significance.

The purposes of this paper are : (i) to review thefindings of research into students ‘ ability to understand,classify and identify rocks; (ii) to suggest reasons whyapproaches to teaching about rocks have provedgenerally ineffective in developing scientific under-standing about rocks; and (iii) to outline a pedagogicapproach and teaching methodology which develops asound conceptual framework about rocks for students .

PREVIOUS RESEARCH

In a study of thirty-four 11-17 year old students fromNew Zealand, Happs (1982) found that the term rockwas used in a non-scientific way. Learners consideredfactors such as physical appearance, shape or weight of asample as critical attributes. Happs found that studentsfrequently indicated that they had heard of rock names,such as ‘granite’, but were unable to identify these rocksfrom the samples provided. He suggested that if theterm ‘rock’ was not understood in its scientific contextthen it would be reasonable to ‘predict that theclassification of rocks and the terms sedimentary,igneous and metamorphic may not be perceived by thestudents in the way that teachers think they might beperceived’ (Happs, 1982). He concluded that children’sviews of rocks are at variance with the Earth scientist’sview (Happs, 1982).

A study of students’ ideas about rocks drawn fromstudents in primary schools in Australia and NewZealand revealed an interest by students in askingquestions about rocks. However, the questions askedand students ‘ speculations about the answers to thosequestions indicated that students had little conceptualunderstanding about rocks (Symington , Biddulph,Happs & Osborne, 1982). In a detailed case-study of 14years old students’ understanding of rocks and minerals, Happs confirmed his earlier researches and found thatstudents did not group rocks in terms of their origin, butsorted according to everyday categories, such as ‘shinyrocks’ and ‘ordinary rocks’ (Happs, 1985). Some 10 yearslater an investigation in seven primary schools in northwest England by the Science Process and ConceptExploration (SPACE) project revealed similar conceptual

Hawley - Building Conceptual Understanding 363

BUILDING CONCEPTUAL UNDERSTANDING IN YOUNG SCIENTISTS

Duncan Hawley Department of Education, University of Wales Swansea, Hendrefoelan,

Swansea, SA2 7NB, Wales, U.K., [email protected]

difficulties held by students aged 5 to 11 years to thoseexposed by the Australasian studies ( Russell et al., 1993). This study found the children used bi-polar criteria inreaching their decisions as to whether or not a specimenwas judged to be a rock, using the attributesrough/smooth, hard/soft, large/small, light/heavy.These criteria were relatively superficial and usedinconsistently. The observation data confirmed thatchildren lacked a meaningful conceptual frameworkwithin which to consider and compare the attributes of arock. The report of the investigation commented, ‘thedecision (about a rock) seemed to be that a rock is ‘all ornothing ‘, ‘a rock is a rock’ rather than thinking about thematerials’ hardness, texture, constituent components,porosity, presence/absence of crystals etc’. The reportsummarises, ‘it would seem that children need toconsider a whole range of common but distinguishablerocks forms and explore similarities and differencesalong a number of dimensions. There is also a case forsome input about techniques and conceptualframeworks which geologists use, providing these areintellectually safe, accessible and practicable.’ (Russell etal. , 1993). However, the SPACE project did not go on tosuggest what input would meet these criteria.

Oversby (1996) conducted an investigation into thelevel of understanding about some key ideas in Earthscience with 139 students aged 9 to 16 years, who hadbeen given some instruction in elementary Earth science,which included investigations and classification of rocks, and 42 post-graduate trainee-teachers, with varyinglevels of scientific background. In response to thequestions “What is a rock ?” and “What is a stone?”, hefound a large proportion of those taking part in theinquiry gave no response, particularly in the 9 to 11 yearage range, The majority of the remaining responsesindicated simplistic notions. The confidence ofrespondents’ ability to answer increased with age, therewas not a corresponding increase in the scientificaccuracy of their answers. This suggests that whileconcepts about rocks had become established, theyremained concepts founded in non-scientific un-derstanding.

In an investigation into the abilities of first-yeartrainee-teachers of science and humanities to identifyrock types Dove (1996) found that the term rock waswidely misunderstood among the trainees. Rocks wereidentified on the basis of feel and color, having seensimilar rocks in the landscape, used as buildingmaterials, or guessing from a list of rocks. In other wordsthe trainees tried to match the rocks with pastexperiences, rather than make any decisions about therock type based on any scientific criteria. Consequentlywhere the perceived characteristics were not met in thespecimens, the rocks went unrecognized.

Independent from the above research, the authorrecognized similar conceptual difficulties in schoolstudents’ understanding about rocks. The authorobserved that students attempt to make sense of rocks ina non-scientific way. Any ability to name a rock sampleresulted from recall, i.e. the matching of a rock sample toa ‘fixed image’ of that rock, usually obtained throughhaving previously seen a photograph or hand specimen

of the rock sample. For example, students who identified a specimen of ‘white granite’ as granite would frequently not be able to recognize a specimen of ‘pink granite’ as agranite. Instead they respond with ‘I don’t know’, orsuggest it is ‘pink rock’, or guess by giving another namethat they know to be a rock. These observations ofstudents’ struggles to make sense of rocks suggest theyhave no clear conceptual framework with which toinvestigate, classify, and associate rocks and rock types.Such an interpretation may also explain the findings ofDove (1996).

DISCUSSION OF TEACHING APPROACHESUSED IN DEVELOPING UNDERSTANDINGABOUT ROCKS

The findings of Dove (1996) and Oversby (1996) are notsurprising in that the teaching methodologies to befound in text books and teaching manuals for studentsaged 7 to 14 years, suggest descriptive-inductiveapproaches to learning about rocks. Commonly, theserecommend that students be given opportunities to ‘sort’ a variety of rock types in different ways. This is done bychoosing simple criteria such as color or shape, and bycomparing and identifying rocks using secondarysources, such as photographs or drawings (for examplesee Nuffield Primary Science, 1995). In arguing that rockidentification is an appropriate skill for primarystudents, Harwood suggests that 10 and 11 year olds canbe expected to move on to distinguishing betweencrystalline and fragmental rocks and to use these criteriain dichotomous keys to identify individual rock samples. The method he suggests students use to gain theseconcepts can be done by placing a dozen different rockson a table and simply asking each individual pupil todivide the rocks into two boxes labelled respectively‘crystalline’ and ‘fragments or grains’, (Harwood, 1987).

In such teaching approaches, there is an assumptionthat students will gradually learn to distinguish betweenthe scientifically most important attributes (definingattributes) and less important characteristics (cor-relational attributes) of a rock through a process of ‘trialand error’ discovery and classification, if they areexposed to a wide range and large number of rockspecimens. This requires students to derive abstractgeneralizations from many individual observations, i.e.an inductive approach. However, as indicated by theexample of students’ difficulty of granite recognition, the inductive approach leads students into compart-mentalising rocks and seeing each rock as singular(Johnston, 1990). Consequently, the inductive approachis poor at helping students recognize the fundamentalgeneric characteristics (defining attributes) thatcategorize different rock groups. So, while a descriptiveapproach may result in the pupil being able to name arock sample at a very specific level, there is littledevelopment in conceptual understanding about howthat rock fits into the scientific scheme of classification ofrocks or the rationale behind it. Such conceptual un-derstanding is imperative if students are to make fullsense of rocks and especially if they are to progress on tomeaningful interpretation of rocks. To enable students to

364 Journal of Geoscience Education, v. 50, n. 4, September, 2002, p. 363-371

scientifically classify rocks into appropriate genericgroups, rather than simply attach a particular name or label to individual rock specimens, students need todevelop generalized concepts of the characteristics ofeach generic rock group. Thus, when confronted withan unfamiliar rock, they have a conceptual framework against which they can compare, hypothesise, test,and modify. As a result, students’ ability to classify,identify, and name rocks is enhanced because rocksare no longer conceptualized as singular entities butas unique specimens (Johnston, 1990) which belong to a wider group of rocks accounted for by general laws.Moreover, the scientific conceptual understandingthey develop will form the basis for questioning,reasoning, speculating, and inferring about rocks.This helps students to understand and predict someof the properties of rocks, such as susceptibility toweathering processes.

The importance of developing such a conceptualframework to enable students to ‘see’ and interpretrocks is outlined by Frodeman (1995). In recognizingthe strong visual component to geological science hestates, ‘Most of us are familiar with the interpretiveaspect of understanding. That is the shift in ourawareness of an object when we approach it with afresh set of concepts or expectations. The outcrop orrock means nothing to the uninitiated until thegeologist introduces concepts for ‘seeing ‘ the rock.’(Frodeman, 1995). Consequently, descriptive-comparative and/or trial and error-discoverylearning methods are inappropriate for effectingsound conceptual understanding about rocks because these approaches leave to chance the prospect ofstudents learning to distinguish between the definingand correlational attributes of rocks. Developing asound conceptual framework about rocks requires apedagogic approach, which enables students toreorganise their perception of the defining andcorrelational attributes of a rock.

A NEW PEDAGOGIC APPROACH

An action research approach was adopted to developa pedagogic approach that would enable students todevelop a sound conceptual framework about rocks.It aimed to devise an intellectually safe, accessible and practicable teaching methodology, grounded in theresponses and reactions of students.

The pedagogic approach described here has beenused successfully with students aged 7 to 11 years, toenable them to classify a range of different rockspecimens into the generic rock groups. In addition,the approach has enabled students to makedeductions about the properties of different rocks.The approach has also been used with students aged11 to 14 years, as a foundation for investigatingprocesses of rock formation. In the case of these olderstudents, two key questions framed the teaching:

(i) ‘What are the key characteristics of different rockgroups?’

(ii) ‘How did the rocks acquire these differentcharacteristics?’.

The second key question builds on knowledge and

understanding, acquired through the teaching meth-odology described here, to facilitate meaningful conceptualprogression in learning about rocks. It leads students to beable to interpret and speculate about the processes offormation of a rock from the textural characteristics ofindividual rock specimens. The approach has also beenused successfully to develop teachers’ understanding ofrocks through initial teacher education programs andIn-Service Training, with the aim that the training betranslated directly into the classroom. Reports by teacherswho have used the approach in the classroom haveconfirmed successful outcomes through using thismethodology.

Organization of teaching materials and students - Thestudents were organized into working groups of about fourstudents for all the stages of the teaching. Each workinggroup was given a range of different rock samples toexamine and classify throughout the stages of the teaching. In the trials described here three examples of igneous rocks,two examples of metamorphic rocks and five examples ofsedimentary rocks were used (Table 1). Most of theexamples used were coarse-grained varieties, whichfacilitated easy observation of the textural characteristics,but the inclusion one medium grained and two fine-grainedsamples provided representatives of rock types with lesseasily observed textures.

Stage 1: 1.1 What is a rock?

This activity aims to clarify students’ perceptions of whatconstitutes a rock and to focus on the idea of a rock beingcomposed of grains.

Students were presented with a tray containing thedifferent rock types and asked to mix and match the rocks to sort them out into groups. When students had completedthis sorting they were asked to explain the reasons why they had grouped the rocks in a particular way. The mostfrequent rationales used to group were color variations,“shininess”, “speckliness” and “roughness”, and occas-ionally the size and shape of specimens presented. Thismight be expected, as both Happs (1982) and Russell et al.(1993) found that students focus on obvious physicalcharacteristics.

1.2 The Question and Answer game

In order to move students to thinking about a morefundamental concept of rocks a word game’ was played.

The teacher explained that some questions would beasked about the way the students had grouped the rocks.One member from each student group was selected andasked to listen carefully to the answers given by theremaining group members. The selected student was askednot to join in the answering, but to identify any word thatseemed to keep appearing in the students ‘responses. When students gave a reason for grouping, e.g. ‘these are allshiny’, the teacher probed their thinking by asking, ‘What is


it that makes them shiny? What can you see in therocks?’. This type of questioning was followed for each of the criteria the students had used for classification. At the end of the questioning the selected pupil was askedwhich word was mentioned most frequently in thestudents’ answers. The result was invariably ‘bits’. It was an easy step to then ask the students ‘What are the rocksare made of?’ and for the students to realise that a rock ismade up of ‘ lots of bits’.

The teacher introduced the term ‘grains’ as thetechnical vocabulary for ‘bits’.

Stage 2: Are there any differences between thegrains of some rocks?

The aim of this activity was to focus students ‘observations on the grains of igneous and sedimentaryrocks. Students were given two rocks, a sample of coarse- grained granite and a sample of coarse-grainedsandstone, and a magnifier. Students were asked toinvent a name for each rock sample, with the intention ofpersonalising the samples and forestalling any desire onbehalf of students to provide a geological name for therocks, which might set up preconceptions. They wereasked to observe and describe the grains of each rocksample. The most frequently noted characteristics were

as in the Stage 1 sorting activity, relating to easilyobservable characteristics. However, many students also observed that the grains in the granite were ‘sharp-edged’, i.e. angular, and the grains of the sandstone were ‘round’. This is an important step in moving towards ascientific understanding of rocks. The overall character-istics of the grains of each sample were drawn outthrough discussion and listed on the board.

Stage 3: Predictions and Explanations

The aim of this activity was to give students concreteexperience from which they could reason about thedifferences between two rock textures.

Students weighed each rock sample of sandstoneand granite to the nearest 0.1g and recorded the results.It was explained that the rocks were to be covered withwater. The students were asked to suggest what theythought would happen to each of the rock samples. They were asked to bear in mind the characteristics of thegrains of each rock type observed earlier. Students thencompletely immersed the rocks into a tub of water andasked to observe what happened. Students reported thatthe sandstone produced bubbles and the granite wasinert. Some students described the bubbles as ‘fizzing’and others as ‘air bubbles’. Students were asked toexplain the presence of the bubbles and two ideas werepredominantly offered:

1) the rock was dissolving (the fizzers);

2) water was rushing in (the air bubblers).

These explanations were presented as alternativehypotheses to the whole class. A class discussionfollowed on how it would be possible to test whichhypothesis is most likely. Students were asked to predictwhether they thought each rock would weigh more,weigh less, or stay the same weight. This gave rise todiscussion about the process of solution and the relativeweight of water compared to air.

After the samples had been immersed for aminimum of five minutes they were re-weighed and theresults for each group were tabulated on the board usinga tally. This strategy allowed any anomalous results to be easily identified and if necessary, further weighing of the specimens. It was noted that the weight of the granitewas unchanged while the sandstone gained afterimmersion in water. In one trial, following the soaking inwater, control samples were re-weighed then left in awarm place overnight. The following day these sampleswere weighed again and students noted that thesandstone had ‘dried out’ and returned to its originalweight. Students were asked to hypothesize on the origin of the extra weight in the sandstone. Responses almostinvariably invoked water as the source of the increasedweight.

The next question asked students to consider howwater penetrated the sandstone. Most responsesinvolved ‘gaps’, ‘tiny holes’, ‘spaces’, ‘air pockets’ and‘air space, which water, has got into’. About 10% ofstudents reasoned ‘there must be air to let the water in’,


Rock Type Rock Group

Granite (grey) Igneous

Granite (red) Igneous

Gabbro Igneous

Schist

(coarse-grained)Metamorphic

Slate Metamorphic

Sandstone(coarse-grained, red) Sedimentary

Sandstone(medium-grained, buff)

Sedimentary

Limestone

(oolitic)Sedimentary

Breccia Sedimentary

Mudstone (red) Sedimentary

Table 1. Rock selected for development of theteaching methodology.

thereby implying displacement. A smaller proportiongave explanations that did not accord with the notion ofadding water to the sample. Students were asked toexplain why the granite did not let water in, and nearlyall answers mentioned ‘no holes to let water in’.

Stage 4: Modelling

This stage of the teaching aimed at helping the studentsunderstand about grain relationships in rocks. Theteacher posed the following questions to the students: (i)how do you get grains to fit together so that there are nospaces between the grains? and (ii) how do you getgrains to fit together so that there are spaces between thegrains?

Students were given a tessellation activity to helpthem answer the questions. Each group of students wasprovided with two sets of gummed paper shapes. Oneset contained rounded shapes (circles and ovoids) andanother set comprised of angular shapes. Both setscontained a variety of sizes. With each set of shapes,students were asked to try to cover a square drawn on apiece of paper. It was emphasised that the shapes mustnot overlap and that they must attempt to cover all thespace (Figure 1). Students quickly realized that it waspossible to fit together the angular shapes to cover thesquare but that the rounded shapes always left spaces.Students were asked to match the rock samples to thegummed shapes which they thought most closelymatched the patterns of the grains in the rock. Allstudents were able to match the rock samples correctly.The teacher introduced the terms interlocking and non-interlocking to describe the different grain relation-ships.

The next step was to develop the concept ofinterlocking and non-interlocking in a three-dimensional form, with the aim of more realistically representingrocks. A Japanese wooden puzzle was used to simulatean interlocking rock. The puzzle consisted of a series ofindividual wooden blocks in a variety of angular shapes,which the students were able to relate to the angulargrains of the interlocking rock. When the puzzle isassembled the pieces interlock to form a cohesiveoctahedron. Glass marbles were used to simulate therounded grains of the non-interlocking rock. These wereplaced in a transparent container and students were ableto observe the pore spaces between the marbles. Theteacher asked the students what they thought wouldhappen when the container was turned upside down.Students were unanimous in their view that ‘the marbleswould fall out’. Inverting the container and allowing themarbles to fall and scatter demonstrated thenon-interlocking nature of the simulated rock. Theteacher noted how the ‘rock’ had ‘fallen to bits’.

Students were asked to examine a sample of aconglomerate, containing rounded pebbles, similar tothe marbles. They were asked to turn the conglomerateupside down and shake the specimen, which remainedintact. The teacher asked the students to suggest whatstops a non-interlocking rock from ‘falling to bits’.Pupils’ suggestions referred to ‘glue’, ‘nature’s glue’,

‘cement’, ‘ mud and clay’, or ‘dried mud’. Cement is thetechnical geological term for the material that fills thepore spaces in sedimentary rocks. In order not to confusestudents with ideas of manufactured cement beingmixed and added to sedimentary rocks the teacher usedthe term ‘rock glue’, drawing analogies withmanufactured glues.

Students were asked to consider how much gluewould be needed to stick the non-interlocking rock.Typically their responses gave suggestions such as, ‘eachgrain would need a little bit where it touches anothergrain’. The concept of lithological cementation was notpursued further. A simulation of the precipitationprocess may have been useful at this point, as somestudents appeared to develop the idea that the ‘rock glue’ needed to be applied drop by drop. A lithificationsimulation would help to clarify the nature of theprocess. Finally, the students were asked to distinguishthe ‘rock glue’ from the constituent grains in a variety ofsedimentary rock samples. First students examined theconglomerate, where the white quartz pebbles could beclearly seen and the distinction was obvious, and then arange of finer-grained sandstones.


Figure 1. Pupil’s example of the tessellationpuzzle (see ‘Stage 4. Modeling’) whichmodels the relationship betweeninterlocking and non-interlocking rocktextures (redrawn).

Stage 5: ‘Crumbliness’ - using understanding tomake inferences

The goal of this activity was to help students see therelationship between the grains in a rock and use thisknowledge to speculate and make inferences about thesusceptibility of different rock types to weatheringprocesses.

Students were presented with a sample of graniteand a sample of sandstone; no technical names wereused, and asked to decide which was interlocking andwhich non-interlocking. All students were able toidentify the texture of these rocks correctly. They werethen asked to suggest which rock might crumble moreeasily, the rock with interlocking grains or the rock withnon-interlocking grains. There was widespreadagreement that the interlocking rock would not crumbleand some divergence of opinion about the non-interlocking rock. The majority of students suggestedthat the sandstone would crumble more easily than thegranite. When asked to explain why, students ‘ responses recognized that the interlocking texture of the granitewould give the rock greater cohesion. Typical responsesincluded ‘the rock will not crumble easily because all thebits are jumbled together and jagged around each otherand it will be difficult for them to drop off because theyare holding each other in place‘, and, ‘the grains in therock fit together so lock in with each other.’

Students were asked to test their hypothesis. Groupsof students were given the two rock samples, a steelteaspoon and a sheet of white paper. They wereinstructed to scrape each rock over the white paper using the spoon. They were to save any bits that crumbled from the rock. As predicted, scraping the sandstone producedgrains and fragments on the paper, while scraping thegranite had no effect on fragmentation. Students wereasked to suggest why the sandstone had ‘crumbled tobits’ and responses generally gave rise to two ideas: (i)the ‘rock glue’ was not very strong and had comeundone, (ii) there was not much ‘rock glue’ holding thegrains together. Most groups of students suggested onlyone of these alternatives, while in all the classes therewere a small number of students who suggested thatboth ideas might explain the crumbliness of thesandstone.

In a follow up discussion students were introducedto different types of ‘rock glue’ through demonstration of three sandstone rocks. One sample had iron oxidecement, another calcium carbonate cement, and a thirdwith silica cement. Students were asked to sort theserocks in order of the strength of the ‘rock glue’. Studentswere also shown one sample of sandstone that was veryporous and another sandstone, which displayed poresfilled with lithological cement. The teacher concludedthis part of the teaching with a summary outlining howboth reasons suggested by the students may be correct.Through discussion, the class devised a list of differentpossible combinations, such as ‘a rock with strong rockglue filling all the spaces’, ‘a rock with strong rock glueonly where grains touch each other ‘, ‘a rock with a weakrock glue filling all the spaces’ and, ‘a rock with weakrock glue only where grains touch each other‘. The

teacher also suggested that some rock glues could bemade weaker by reacting with water, as in somesynthetic glues. With some classes, the concept of rockporosity was taken further. Students were asked toconsider the implications of ‘rock-locking’ and‘rock-glueing’ for constructing a well.

Stage 6: Classifying rocks: the Earth scientist’s way

This stage of the teaching aimed to (i) consolidatestudents’ new understanding about grain relationshipsin rocks, (ii) to introduce the concept of grainarrangement, and (iii) to allow students to classify aselection of rocks using the newly formed conceptualframework. Students’ learning was summarised by theteacher using a diagram as an aide-memoir (Figure 3),which focussed the students’ observations on two keycharacteristics: (i) grain relationships, (ii) grainarrangement.

6.1 Grain relationships

The teacher reviewed the importance and significance ofdetermining by observation how the grains of the rock fittogether to distinguish between interlocking andnon-interlocking textures. The usefulness of grain shapein helping to make this decision was outlined. Thelimitations of this observation were discussed, demon-strating with samples how a non-interlocking rock might contain angular grains with pore spaces filled or partially filled with ‘rock glue’. Through the concepts developedby the practical activities and investigations earlier in theteaching, students were able to sort a selection of rockswith little difficulty into two groups, (i) crystalline rocksand (ii) fragmental rocks. However, the fine-grained rock specimens caused some uncertainty, with studentsfrequently placing them in a separate group orpositioning them tentatively on the periphery of one ofthe groups.

6.2 Grain arrangement

The second key observation expanded students’understanding of the importance of observing rockcharacteristics at grain level and introduced the conceptof grain arrangement. Two forms of arrangement wereintroduced: (i) random, and (ii) aligned, illustrated onthe ‘Looking at Rocks like a Geologist’ worksheet (Figure 2). Samples of granite and schist were used to demon-strate the differences. To focus on recognizing thedifferent arrangement of the grains in the granite and theschist, students completed a labelled sketch of each rocksample. A rectangular hole, 1 cm by 1.5 cm, provided aframe and a magnifying glass was used to enable thestudents to make precise observations (Figure 3).

6.3 Classifying rocks

In the final teaching activity the students were given anassortment of rock samples (see Table 1) and asked toarrange them into different types of rocks using the



Figure 2. Worksheet used to help students focus their observations in classifyinga range of rocks.

principles learned from their investigations. Studentswere allowed to use the ‘Looking at rocks like a geologist ‘worksheet (Figure 2), if they wished.

All students showed confidence in undertaking thisactivity and most of the rocks presented little difficulty. Initially the rocks were sorted into interlocking andnon-interlocking types. The first rocks to be categorizedthis way were the granite and the coarse-grained redsandstone. This was undoubtedly because of familiarityfrom earlier investigations. Groups of students adopteddifferent strategies for making their decisions. Somestudents carefully observed the grains of each rock andthen made an independent decision about its type, whileother students used the worksheet (Figure 2) as areference for making their decision. A smaller number ofstudents used the two ‘key’ rocks, the granite and thecoarse-grained red sandstone, for reference andcomparison. In most cases the interlocking rocks werethen sub-divided according to grain arrangement.

Two rocks seemed more problematical to thestudents, the slate and the red mudstone. After initial

inspection these rocks were almost always placed to oneside and revisited after all the other rocks had beenexamined and sorted. This is not surprising as it is notpossible to see the grains clearly because of theirfine-grained character, thereby removing the main basisof observation and classification. Some studentsseparated these rocks in two distinct categories. Othersplaced them in a tentative holding group and theseadmitted to being puzzled as to how to categorize thesesamples, realising they could not see the grains. A smallproportion of students placed these rocks according tocolor, the red mudstone being placed alongside the redsandstone and the slate alongside the gabbro. To solvethis problem students were asked to draw upon theirknowledge about ‘crumbliness’ and grain relationshipsand test the fine-grained rocks by scraping. This allowedall students to make inferences about the category of rock to which the fine-grained samples belonged. Studentswere asked how an Earth scientist could confirm theresults of such an inference and two suggestions wereprevalent: (i) ‘soaking the rocks and weighing’, and (ii)‘putting the rocks under a microscope’. This indicatedthat students had grasped the importance of the texturalrelationships of grains in identifying rocks.

Overall, a significant majority of students con-fidently sorted the rocks into three categories.Furthermore, when asked why they thought rocksbelonged to a particular category students were able tooffer clear explanations which focussed on the differenttextural characteristics of the grains At this stage theteacher introduced the names Igneous, Sedimentary andMetamorphic for the three groups of rocks. , Studentsthen produced name labels for each group. In a fewclasses, students were asked to subdivide rocks withineach of the three groups. No instruction was given fromthe teacher. Interestingly, most students used grain sizeas the major criterion for sub-division. This suggests theconcepts of rocks being constituted of grains and theimportance of grain relationships had been firmlyplanted in students’ minds. In addition, some studentsbegan to sort using the color of the grains, thereby layingthe foundations for exploring the idea of differentmineral content. Finally, these classes were given formalidentification keys, allowing the students routes throughwhich they could find the specific names of rocks.Students found their way through the keys with minimal support from the teacher, easily equating the termcrystalline with interlocking textures and fragmentalwith non-interlocking textures.

SUMMARY

The pedagogic approach described here resulted inyoung students learning to determine, recognize andexplain fundamental textural differences in a range ofrocks, equivalent to the key textural characteristics ofigneous, sedimentary, and metamorphic rocks.Furthermore, students were able to relate thesecharacteristics to a range of rock properties. They arrivedat this understanding through a series of practicalactivities and observations, which tested and modifiedtheir speculations about the characteristics of rocks. The


Figure 3. Example of pupil’s observations anddrawings to highlight the differencebetween random grain orientation in an igneous rock and parallel grain orien-tation in a metamorphic rock (re-drawn).

results of this work demonstrate that this investigativeapproach, which focuses on grain relationships in rocks,develops students’ ability to meaningfully generalizeabout the abstract relations of rock groups in the wayrequired for making sense of rocks scientifically. Inachieving this, the teaching methodology fulfils the keyrecommendations drawn from the investigationsoutlined in the Science Concept and Concept Exploration project (Russell et al , 1993) to provide ‘input abouttechniques and conceptual frameworks which geologists use’, which are ‘intellectually safe, accessible andpracticable.’

REFERENCES

Dove, J.E., 1996, Student identification of rock types,Journal of Geoscience Education, v. 44, p. 266-269.

Department for Education and Employment and theQualifications and Curriculum Authority, 1999,National Curriculum, London, HMSO, 83p.

Frodeman, R., 1995, Geological Reasoning: Geology as an interpretive and historical science, GeologicalSociety of America Bulletin, v. 107, p. 960-968.

Happs, J.C., 1982, Rocks and Minerals, LISP WorkingPaper 20, University of Waikato, Hamilton, NewZealand.

Happs, J.C., 1985, Regression on learning outcomes:Some examples from the earth sciences, EuropeanJournal of Science Education, v. 7 , p. 431-443.

Harwood, D., 1987, Rock identification: An appropriateskill for ten to eleven year olds?, Geology Teaching12, p. 58-67.

Johnston, R.J., 1990, Philosophy, Ideology andGeography, p. 48 -66 in Gregory, Derek and Walford, Rex, editors, Horizons in Human Geography:London, Macmillan Education, 426 p.

Nuffield Primary Science, 1995, Science Processes andConcept Exploration, Ages 7-12, Rocks, Soil andWeather, Teacher’s Guide, 1995 Curriculum:London, Collins Educational for the NuffieldChelsea Curriculum Trust. 96 p.

Oversby, J., 1996, Knowledge of earth science and thepotential for its development, School ScienceReview, v.78, p. 91-96.

Russell, T., Bell, D., Longden, K. and McGuigan, L., 1993,Rocks, Soil and Weather, Primary SPACE projectresearch report, Liverpool, Liverpool UniversityPress, 174 p.


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BUILDING CONCEPTUAL UNDERSTANDING IN … of research into students ‘ ability to understand, classify and identify rocks; (ii) to suggest reasons why approaches to teaching about