GCSE WORKSHEET – TEACHER'S GUIDE
ST PANCRAS GARDENS – ROCK TYPES TEACHER’S GUIDE This guide provides answers to the questions posed in the pupil’s worksheet and also offers suggestions for future work back in the classroom or as individual projects for students. 1 LIMESTONE Before beginning, ensure that pupils have the following: Map of St Pancras Gardens Two sheets of fossils Two colouring pencils There are two distinctly different types of limestone within the gardens – Portland Limestone and Carboniferous Limestone. Each one contains a unique group of fossils that can be used to identify it. You have been given two sheets of paper that list some of the fossils found in each. A number of unshaded gravestones are also marked on your map. These are made of either one of the two limestones. Locate these gravestones and try to determine their lithology (rock type) by finding as many of the listed fossils in each one as you can. Choose a different colour for each type of limestone and colour in the unshaded gravestones on your map according to your findings. Don’t forget to colour in your key too! LOOK at the fossils carefully. Draw what you see and label any features you can using the sketches provided. THINK about what you are looking at… What do these fossilized creatures remind you of? Where do you think they might have lived? (answer on your notes pages) They look like shells that you find on the beach. This suggests that they once lived in the sea. What does this tell you about how the limestones were formed? (answer on your notes pages) The limestones were formed by the deposition and consolidation of fossilized creatures like those seen here. 2 MARBLE Marbles are limestones that have been altered by high temperatures and/or pressures. This process is known as METAMORPHISM, and marble is a METAMORPHIC rock. There are a few examples of marble within St Pancras Gardens, but don’t be misled by the information plaques on some of the memorials because the word marble is used by stonemasons to mean any rock that can take a polish, which is not the same definition as a geologist would give! Compare the marble of the Tate Family Grave with the limestone of the Ann Abbey Memorial (see map). How are they similar? How are they different? Colour (try to find relatively clean surfaces) ________________________________________________________________ ___Both are creamy white in colour, but the limestone has a more grey appearance than the marble_________________________________________ Fossil content (don’t try and identify anything, just look at numbers!) ________________________________________________________________ ___The limestone grave has distinct bands of fossils running horizontally across it, whereas the marble grave has no visible fossils at all____________________ Surface weathering (which has a rougher, more eroded-looking surface?) ________________________________________________________________ ___The limestone Ann Abbey Memorial has a much rougher surface where it has been eroded unevenly. The marble is much smoother______________________ Texture (are they smooth? rough? crystalline? grainy?) ________________________________________________________________ ___The limestone is quite rough and visibly grainy. The marble is much smoother and has a crystalline texture__________________________________ 3 GRANITE What type of rock is granite? (circle correct answer) SEDIMENTARY IGNEOUS METAMORPHIC Mineralogy Quartz is otherwise known as SILICON DIOXIDE. What is its chemical formula? _____SiO2______ Grain size Using a ruler, measure the lengths of 5 feldspar crystals (use feldspar crystals because they have the most regular shape and distinct long axes that can be easily compared): Length of feldspar crystal: 1 ___________ Average: 2 ___________ _____ + _____ + _____ + _____ + _____ 5 3 ___________ 4 ___________ 5 ___________ = _____mm From your average feldspar crystal length, do you think this is a coarse, medium or fine grained rock? Why? _______________Granites are coarse grained because the crystals grew slowly from the melt as an intrusive rock, whereas an extrusive rock, e.g. a basalt would be fine grained because it cooled more quickly_______________ Xenoliths Can you see any patches within the granite that look different from the surrounding rock? (If you are at the Rhodes Family Grave you may not, so try one of the other granite stones marked on your map). What distinguishes them from the rest of the granite? ______________They are darker in colour and finer grained________________ What shape are they? ___________They are irregular in shape and rounded at the edges___________ (Check that it is not dirt or lichen that you are looking at!) These are XENOLITHS (Greek word for “strange rock”). Xenoliths are blocks of country rock (the rock into which the granite would have been intruded when molten) that were dislodged by the intrusion and “fell” into the hot magma. Originally the blocks would have been angular in shape but became more rounded as they were eroded by the hot magma (i.e. the edges melted). Draw an example of a xenolith, noting its size and its rounded edges. Try to point out how it is different from the surrounding granite, but don’t worry about its mineral content! XENOLITH SKETCH 4 SANDSTONE Sandstone is formed by the cementing together of grains of sand. Does this make it sedimentary, igneous or metamorphic? ______Sedimentary_______ Would you say that this sandstone is coarse grained, medium grained or fine grained? (use the same criteria that you did for granite) _________Medium grained___________ Make your way to William Jones’ gravestone (see map)… This gravestone has very well defined bedding planes. (Bedding = a series of visible layers in a rock that reflect the original surfaces of deposition) Has the gravestone been cut parallel or perpendicular to these bedding planes? ______Parallel to the bedding planes______ Weathering tends to concentrate along the planes of weakness between sandstone layers (bedding planes). As a result, large flakes of sandstone are detached from the surface, leaving it very uneven. Bedding planes Ασκδϕφησαδη;ασηγ;οηα σδγηοασηγ ασα;σοδφηαο σηδα σδγ ηγασηγησ αδ η σαγ ηασοδγη ασοιηγ ηγ ο αησ οσηδγ ασηγ ασιηδγο ηασ γηασγ αση σσηγοαη σδη αοσιδαοσηδγησγ ιηα αακσδϕηφασυηδ ασδγηα σοδηγοιασδγη αισηγδιοη ασγ οασδηγιοαησγιοηαα Make a sketch of the whole gravestone, marking on the bedding planes and eroded surfaces: GRAVESTONE SKETCH Eroded surfaces Bedding planes Don’t forget to add a scale! And finally… Using your map, make your way to the Burdett-Coutts Memorial Sundial. Then complete the diagram using terms from the list below: PINK GRANITE MANSFIELD SANDSTONE MARBLE PORTLAND LIMESTONE GREY GRANITE CAST IRON GREY GRANITE PINK GRANITE CAST IRON MARBLE RED MANSFIELD SANDSTONE PORTLAND LIMESTONE KEY Portland Limestone Carboniferous Limestone St Pancras Hospital Railway William Jones’ Grave (SANDSTONE) Soane Mausoleum (LIMESTONE & MARBLE) Flaxman Family Vault (LIMESTONE) Jane Grundy Memorial (PINK GRANITE) Burdett Coutts Sundial Tate Family Grave (MARBLE) St Pancras Hospital The Hardy Tree Drinking fountain Portland Lst Carboniferous Lst Ann & William Birch’s Grave (GREY GRANITE) Ann Abbey Portland Lst Memorial (LIMESTONE) St Pancras Old Church Portland base & Carboniferous lid Rhodes Family Grave (PINK & GREY GRANITE)
© Copyright 2024