Rocks
16 Grade 10 Geography questions on Rocks, with worked marking schemes. 16 questions are available on this topic in full.
Question 1
2 marksDistinguish between intrusive igneous rocks and extrusive igneous rocks.
(2 marks)
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3 marksState three characteristics of metamorphic rocks.
(3 marks)
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1 markThe limestone quarried near Bamburi for the manufacture of cement was formed mainly through the
A. evaporation of sea water trapped in a hot, shallow basin
B. cooling and hardening of lava that flowed into the shallow sea
C. cementing together of sand grains blown inland by the monsoon winds
D. accumulation and compaction of shells and skeletons of sea creatures
(1 mark)
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5 marksDescribe how a sedimentary rock such as sandstone is formed from materials carried by a river.
(5 marks)
Marking scheme
Award 1 mark per correct stage, in a logical sequence. Max 5 marks. - Rocks on the land are broken down by weathering into small particles such as sand and gravel. (1) - The loose particles are eroded and transported by the river. (1) - The river loses energy at its lower course or where it enters a lake or the sea and deposits the load. (1) - The material settles in horizontal layers, with later deposits burying earlier ones over a long period. (1) - The weight of the overlying layers compacts the particles, squeezing out water. (1) - Dissolved minerals cement the particles together to form a solid rock. (1)
Question 5
4 marksIdentify the mineral or rock that is mined at each of the following places in Kenya: (a) Kariandusi (b) Kerio Valley (c) Kwale (d) Taita Taveta.
(4 marks)
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6 marksExplain three ways in which rocks are important to farming in Kenya.
(6 marks)
Marking scheme
Award 1 mark for the way identified and 1 mark for the explanation. Three ways required. Max 6 marks. - Rocks are the parent material of soil (1); as rocks weather they break down to form the soil in which crops such as maize and tea are grown (1). - Rocks release mineral nutrients on weathering (1); volcanic rocks in areas such as the central highlands weather into deep, fertile soils that support high crop yields (1). - Some rocks are used to correct soil conditions (1); limestone is ground and applied to acidic soils to raise the pH so that crops can take up nutrients (1). - Porous rocks store underground water (1); this water is tapped through boreholes and wells for irrigation and for watering livestock in dry areas such as Kajiado (1). - Bare rock outcrops act as rock catchments (1); rain water running off them is harvested into pans and tanks and used to water livestock and to irrigate kitchen gardens in dry areas (1). Accept any three well-explained ways.
Question 7
1 markA learner is grouping rock samples collected during a field study. Which pair contains only sedimentary rocks?
A. Limestone and shale
B. Granite and slate
C. Basalt and marble
D. Gneiss and pumice
(1 mark)
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3 marksSuggest three measures that could be taken to reduce the environmental damage caused by quarrying of building stone in Kenya.
(3 marks)
Marking scheme
Award 1 mark for each sensible measure. Max 3 marks. - Refilling and levelling abandoned quarries and planting trees or grass on them. (1) - Converting worked-out pits into fish ponds or water reservoirs instead of leaving them open. (1) - Requiring an environmental impact assessment and a licence before a quarry is opened. (1) - Sprinkling water on quarry roads and working faces to control dust pollution. (1) - Restricting blasting to set hours to reduce noise and vibration damage to nearby homes. (1) - Treating and settling water pumped out of quarries before releasing it into rivers. (1)
Question 9
1 markIn a lesson on the rock cycle, a learner states that shale buried deeply in the crust turns directly into an igneous rock. The correct position is that shale
A. cannot change into any other type of rock once it has been formed
B. can only change into another rock after it has been exposed and weathered at the surface
C. becomes an igneous rock as soon as it is compressed by the layers lying above it
D. must first melt into magma, which then cools and solidifies before an igneous rock is formed
(1 mark)
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1 markSoapstone carved into ornaments at Tabaka in Kisii County was formed when an older rock was altered deep in the crust by great heat and pressure without melting. To which group of rocks does soapstone belong?
A. Extrusive igneous rocks
B. Intrusive igneous rocks
C. Metamorphic rocks
D. Chemically formed sedimentary rocks
(1 mark)
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1 markGranite quarried in the Machakos area is made up of large crystals that can easily be seen with the naked eye. This texture shows that the magma from which the granite formed
A. cooled slowly over a long time deep below the earth's surface
B. cooled very quickly after pouring out onto the earth's surface
C. was squeezed by great pressure after the rock had already formed
D. was deposited in layers by running water before it hardened
(1 mark)
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1 markWhich of the following correctly matches a rock with the metamorphic rock that forms from it?
A. Marble changes into sandstone
B. Granite changes into limestone
C. Clay changes into gneiss
D. Sandstone changes into quartzite
(1 mark)
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1 markDuring a field study near Naivasha, a learner picks up a rock that is very light and floats when placed in water. The best explanation for this property is that
A. gases escaping from the lava left many air spaces inside the rock
B. the rock was formed deep inside the crust under heavy pressure
C. the rock holds a large amount of water inside it
D. the minerals in the rock dissolve as soon as they touch water
(1 mark)
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3 marksExplain how limestone is changed into marble when a mass of magma intrudes into it.
(3 marks)
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4 marksAccount for the wide occurrence of volcanic rocks in the floor of the Rift Valley in Kenya.
(4 marks)
Marking scheme
Award 1 mark per correct point. Max 4 marks. - The area lies along a major zone of crustal weakness where the crust was stretched and faulted. (1) - The faults and fractures created lines of weakness that reached down to the molten material below. (1) - Magma was forced up through these fractures and poured out onto the surface as lava. (1) - Eruptions have been repeated over a long period, so successive lava flows covered the floor and flanks of the valley. (1) - Explosive eruptions also threw out ash and volcanic dust, which settled and consolidated into rocks such as tuff. (1) - Volcanic activity is still going on in the area, for example at Longonot and Menengai, so fresh volcanic material continues to be added. (1)
Question 16
1 markTrona, from which soda ash is produced at Lake Magadi, was formed when
A. dissolved salts were left behind as the lake water evaporated under high temperatures
B. dust blown from the surrounding plains settled and was cemented at the lake shore
C. hot lava flowed into the lake and cooled rapidly on the lake floor
D. the remains of fish and water weeds were buried and compressed on the lake bed
(1 mark)
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